The role of junctional adhesion molecules in vascular inflammation

Role of the endothelium in inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are a complex group of diseases involving alterations in mucosal immunity and gastrointestinal physiology during both initiation and progressive phases of the disease. At the core of these alterations are endothelial cells, whose continual adjustments in structure and function coordinate vascular supply, immune cell emigration, and regulation of the tissue environment. Expansion of the endothelium in IBD (angiogenesis), mediated by inflammatory growth factors, cytokines and chemokines, is a hallmark of active gut disease and is closely related to disease severity. The endothelium in newly formed or inflamed vessels differs from that in normal vessels in the production of and response to inflammatory cytokines, growth factors, and adhesion molecules, altering coagulant capacity, barrier function and blood cell recruitment in injury. This review examines the roles of the endothelium in the initiation and propagation of IBD pathology and distinctive features of the intestinal endothelium contributing to these conditions.

An expression system for screening of proteins for glycan and protein interactions

Here we describe a versatile high-throughput expression system that permits genome-wide screening of type 1 membrane and secreted proteins for interactions with glycans and proteins using both cell-expressed and soluble forms of the expressed proteins. Based on Gateway cloning methodology, we have engineered a destination vector that directs expression of enhanced green fluorescent protein (EGFP)-tagged proteins at the cell surface via a glycosylphosphatidylinositol tail. The EGFP fusion proteins can then be cleaved with PreScission protease to release soluble forms of proteins that can be optionally biotinylated. We demonstrate the utility of this cloning and expression system for selected low-affinity membrane lectins from the siglec family of sialic acid-binding immunoglobulin-like lectins, for the glycosaminoglycan-binding proteins FGF-1 and BACE, and for the heterotypic adhesion molecules JAM-B and JAM-C. Cell-expressed proteins can be evaluated for glycan interactions using polyvalent soluble glycan probes and for protein interactions using either cells or soluble proteins. Following cleavage from the cell surface, proteins were complexed in solution and sufficient avidity was achieved to measure weak protein–glycan and weak protein–protein interactions using glycan arrays and surface plasmon resonance, respectively.

Zebrafish as a model for hemorrhagic stroke

Blood vessels perform the fundamental role of providing conduits for the circulation of oxygen and nutrients and the removal of waste products throughout the body. Disruption of tissue perfusion by ischemia or hemorrhage of blood vessels has a range of devastating consequences including stroke. Stroke is a complex trait that includes both genetic and environmental risk factors. The zebrafish is an attractive model for the study of hemorrhagic stroke due to the conservation of the molecular mechanisms of blood vascular development among vertebrates and the experimental advantages that can be applied to zebrafish embryos and larva. This chapter will focus on the maintenance of vascular integrity and some of the seminal experimentation carried out in the zebrafish.

Morphology and properties of brain endothelial cells

The molecular advances in various aspects of brain endothelial cell function in steady states are considerable and difficult to summarize in one chapter. Therefore, this chapter focuses on endothelial permeability mechanisms in steady states and disease namely vasogenic edema. The morphology and properties of caveolae and tight junctions that are involved in endothelial permeability to macromolecules are reviewed. Endothelial transport functions are briefly reviewed. Diseases with alterations of endothelial permeability are mentioned and details are provided of the molecular alterations in caveolae and tight junctions in vasogenic edema. Other factors involved in increased endothelial permeability such as the matrix metalloproteinases are briefly discussed. Of the modulators of endothelial permeability, angioneurins such as the vascular endothelial growth factors and angiopoietins are discussed. The chapter concludes with a brief discussion on delivery of therapeutic substances across endothelium.

Age and 17β-estradiol effects on blood-brain barrier tight junction and estrogen receptor proteins in ovariectomized rats

Age and estrogen levels alter blood-brain barrier (BBB) tight junction (TJ) regulation, impacting brain homeostasis and pathological outcomes. This examination evaluated BBB TJ and estrogen receptor (ER) protein expression changes in young (8-10 week) and middle-aged (10-12 month) ovariectomized female Fisher-344 rats with chronic 17β-estradiol or placebo treatment. Middle-aged rats showed decreased protein expression of occludin with 17β-estradiol (55 kDa band) or placebo (45, 55, 60 kDa bands) treatment compared to respective young. In young animals, 17β-estradiol treatment increased expression of the occludin 55 kDa band over placebo; however, this effect was lost in the middle-aged animals. In both young and middle-aged animals, expression of claudin-5 (23, 32 kDa bands) and ERα (66 kDa) increased with 17β-estradiol treatment, while junctional adhesion molecule-A showed no change across all groups. However, ERα expression (66 kDa) was significantly reduced in the middle-aged animals compared to young placebo treated animals. Measurement of BBB TJ permeability via in situ perfusion of (14)C-sucrose showed no change with age or treatment. Our results show that increasing age and 17β-estradiol treatment alters the expression of ERα and distinct BBB TJ protein isoforms without altering functional paracellular permeability.

Targeting the recruitment of monocytes and macrophages in renal disease

Macrophages convert proinflammatory or anti-inflammatory signals of tissue microenvironments into response mechanisms. These response mechanisms largely derive from evolutionary conserved defense programs of innate host defense, wound healing, and tissue homeostasis. Hence, in many settings these programs lead to renal inflammation and tissue remodeling (ie, glomerulonephritis and sclerosis or interstitial nephritis and fibrosis). There is abundant experimental evidence that blocking macrophage recruitment or macrophage activation can ameliorate renal inflammation and fibrosis. In this review we discuss experimental tools to target renal macrophage recruitment by using antagonists against selectins, chemokines, integrins, or other important cytokines that mediate renal injury via macrophage recruitment, some of these already having been used in clinical trials.

Force-induced formation and propagation of adhesion nanodomains in living fungal cells

Understanding how cell adhesion proteins form adhesion domains is a key challenge in cell biology. Here, we use single-molecule atomic force microscopy (AFM) to demonstrate the force-induced formation and propagation of adhesion nanodomains in living fungal cells, focusing on the covalently anchored cell-wall protein Als5p from Candida albicans. We show that pulling on single adhesins with AFM tips terminated with specific antibodies triggers the formation of adhesion domains of 100-500 nm and that the force-induced nanodomains propagate over the entire cell surface. Control experiments (with cells lacking Als5p, single-site mutation in the protein, bare tips, and tips modified with irrelevant antibodies) demonstrate that Als5p nanodomains result from protein redistribution triggered by force-induced conformational changes in the initially probed proteins, rather than from nonspecific cell-wall perturbations. Als5p remodeling is independent of cellular metabolic activity because heat-killed cells show the same behavior as live cells. Using AFM and fluorescence microscopy, we also find that nanodomains are formed within ∼30 min and migrate at a speed of ∼20 nm·min(-1), indicating that domain formation and propagation are slow, time-dependent processes. These results demonstrate that mechanical stimuli can trigger adhesion nanodomains in fungal cells and suggest that the force-induced clustering of adhesins may be a mechanism for activating cell adhesion.

Evaluation of soluble junctional adhesion molecule-A as a biomarker of human brain endothelial barrier breakdown

BACKGROUND

An inducible release of soluble junctional adhesion molecule-A (sJAM-A) under pro-inflammatory conditions was described in cultured non-CNS endothelial cells (EC) and increased sJAM-A serum levels were found to indicate inflammation in non-CNS vascular beds. Here we studied the regulation of JAM-A expression in cultured brain EC and evaluated sJAM-A as a serum biomarker of blood-brain barrier (BBB) function.

METHODOLOGY/PRINCIPAL FINDINGS

As previously reported in non-CNS EC types, pro-inflammatory stimulation of primary or immortalized (hCMEC/D3) human brain microvascular EC (HBMEC) induced a redistribution of cell-bound JAM-A on the cell surface away from tight junctions, along with a dissociation from the cytoskeleton. This was paralleled by reduced immunocytochemical staining of occludin and zonula occludens-1 as well as by increased paracellular permeability for dextran 3000. Both a self-developed ELISA test and Western blot analysis detected a constitutive sJAM-A release by HBMEC into culture supernatants, which importantly was unaffected by pro-inflammatory or hypoxia/reoxygenation challenge. Accordingly, serum levels of sJAM-A were unaltered in 14 patients with clinically active multiple sclerosis compared to 45 stable patients and remained unchanged in 13 patients with acute ischemic non-small vessel stroke over time.

CONCLUSION

Soluble JAM-A was not suited as a biomarker of BBB breakdown in our hands. The unexpected non-inducibility of sJAM-A release at the human BBB might contribute to a particular resistance of brain EC to inflammatory stimuli, protecting the CNS compartment.

Network analysis of transcriptional regulation in response to intramuscular interferon-β-1a multiple sclerosis treatment

Interferon-β (IFN-β) is one of the major drugs for multiple sclerosis (MS) treatment. The purpose of this study was to characterize the transcriptional effects induced by intramuscular IFN-β-1a therapy in patients with relapsing-remitting form of MS. By using Affymetrix DNA microarrays, we obtained genome-wide expression profiles of peripheral blood mononuclear cells of 24 MS patients within the first 4 weeks of IFN-β administration. We identified 121 genes that were significantly up- or downregulated compared with baseline, with stronger changed expression at 1 week after start of therapy. Eleven transcription factor-binding sites (TFBS) are overrepresented in the regulatory regions of these genes, including those of IFN regulatory factors and NF-κB. We then applied TFBS-integrating least angle regression, a novel integrative algorithm for deriving gene regulatory networks from gene expression data and TFBS information, to reconstruct the underlying network of molecular interactions. An NF-κB-centered sub-network of genes was highly expressed in patients with IFN-β-related side effects. Expression alterations were confirmed by real-time PCR and literature mining was applied to evaluate network inference accuracy.

Unravelling the mechanism and significance of thrombin binding to platelet glycoprotein Ib

The main question concerning the mechanism of a-thrombin binding to platelet membrane glycoprotein (GP)Ib is whether it involves both thrombin exosite I and exosite II. The solution of two independent crystal structures suggests alternative explanations that may actually reflect different modes of binding with distinct pathophysiological significance. With respect to function, it is still unclear whether thrombin binding to GPIb promotes procoagulant and prothrombotic pathways of response to vascular injury or limits such responses by sequestering, at least temporarily, the active enzyme. We review here published information on these topics and touch upon ongoing studies aimed at finding definitive answers to outstanding questions relevant for a better understanding of thrombosis and haemostasis.

Clinical and experimental pancreatic islet transplantation to striated muscle: establishment of a vascular system similar to that in native islets

OBJECTIVE

Curing type 1 diabetes by transplanting pancreatic islets into the liver is associated with poor long-term outcome and graft failure at least partly due to inadequate graft revascularization. The aim of the current study was to evaluate striated muscle as a potential angiogenic site for islet transplantation.

RESEARCH DESIGN AND METHODS

The current study presents a new experimental model that is found to be applicable to clinical islet transplantation. Islets were implanted into striated muscle and intraislet vascular density and blood flow were visualized with intravital and confocal microscopy in mice and by magnetic resonance imaging in three autotransplanted pancreatectomized patients. Mice were rendered neutropenic by repeated injections of Gr-1 antibody, and diabetes was induced by alloxan treatment.

RESULTS

Contrary to liver-engrafted islets, islets transplanted to mouse muscle were revascularized with vessel densities and blood flow entirely comparable with those of islets within intact pancreas. Initiation of islet revascularization at the muscular site was dependent on neutrophils, and the function of islets transplanted to muscle was proven by curing diabetic mice. The experimental data were confirmed in autotransplanted patients where higher plasma volumes were measured in islets engrafted in forearm muscle compared with adjacent muscle tissue through high-resolution magnetic resonance imaging.

CONCLUSIONS

This study presents a novel paradigm in islet transplantation whereby recruited neutrophils are crucial for the functionally restored intraislet blood perfusion following transplantation to striated muscle under experimental and clinical situations.

New aspects of the molecular constituents of tissue barriers

Epithelial and endothelial tissue barriers are based on tight intercellular contacts (Tight Junctions, TJs) between neighbouring cells. TJs are multimeric complexes, located at the most apical border of the lateral membrane. So far, a plethora of proteins locating at tight intercellular contacts have been discovered, the role of which has just partly been unraveled. Yet, there is convincing evidence that many TJ proteins exert a dual role: They act as structural components at the junctional site and they are involved in signalling pathways leading to alterations of gene expression and cell behaviour (migration, proliferation). This review will shortly summarize the classical functions of TJs and TJ-related proteins and will introduce a new category, termed the "non-classical" functions of junctional proteins. A particular focus will be directed towards the nuclear targeting of junctional proteins and the downstream effects elicited by their intranuclear activities.

Sertoli-germ cell junctions in the testis: a review of recent data

Spermatogenesis is a process that involves an array of cellular and biochemical events, collectively culminating in the formation of haploid spermatids from diploid precursor cells known as spermatogonia. As germ cells differentiate from spermatogonia into elongated spermatids, they also progressively migrate across the entire length of the seminiferous epithelium until they reach the luminal edge in anticipation of spermiation at late stage VIII of spermatogenesis. At the same time, these germ cells must maintain stable attachment with Sertoli cells via testis-unique intermediate filament- (i.e. desmosome-like junctions) and actin- (i.e. ectoplasmic specializations, ESs) based cell junctions to prevent sloughing of immature germ cells from the seminiferous epithelium, which may result in infertility. In essence, both desmosome-like junctions and basal ESs are known to coexist between Sertoli cells at the level of the blood-testis barrier where they cofunction with the well-studied tight junction in maintaining the immunological barrier. However, the type of anchoring device that is present between Sertoli and germ cells depends on the developmental stage of the germ cell, i.e. desmosome-like junctions are present between Sertoli and germ cells up to, but not including, step 8 spermatids after which this junction type is replaced by the apical ES. While little is known about the biology of the desmosome-like junction in the testis, we have a relatively good understanding of the molecular architecture and the regulation of the ES. Here, we discuss recent findings relating to these two junction types in the testis, highlighting prospective areas that should be investigated in future studies.

A disintegrin and metalloprotease 10 is a novel mediator of vascular endothelial growth factor-induced endothelial cell function in angiogenesis and is associated with atherosclerosis

OBJECTIVE

To elucidate the downstream mechanisms of vascular endothelial growth factor receptor 2 (VEGFR2), a key receptor in angiogenesis, which has been associated with atherosclerotic plaque growth and instability.

METHODS AND RESULTS

By using a yeast-2-hybrid assay, we identified A Disintegrin And Metalloprotease 10 (ADAM10) as a novel binding partner of VEGFR2. ADAM10 is a metalloprotease with sheddase activity involved in cell migration; however, its exact function in endothelial cells (ECs), angiogenesis, and atherosclerosis is largely unknown. For the first time to our knowledge, we show ADAM10 expression in human atherosclerotic lesions, associated with plaque progression and neovascularization. We demonstrate ADAM10 expression and activity in ECs to be induced by VEGF; also, ADAM10 mediates the ectodomain shedding of VEGFR2. Furthermore, VEGF induces ADAM10-mediated cleavage of vascular endothelium (VE)-cadherin, which could increase vascular permeability and facilitate EC migration. Indeed, VEGF increases vascular permeability in an ADAM10- and ADAM17-dependent way; inhibition of ADAM10 reduces EC migration and chemotaxis.

CONCLUSIONS

These data provide the first evidence of ADAM10 expression in atherosclerosis and neovascularization. ADAM10 plays a functional role in VEGF-induced EC function. These data open perspectives for novel therapeutic interventions in vascular diseases.

The overlap between neurodegenerative and vascular factors in the pathogenesis of dementia

There is increasing evidence that cerebrovascular dysfunction plays a role not only in vascular causes of cognitive impairment but also in Alzheimer's disease (AD). Vascular risk factors and AD impair the structure and function of cerebral blood vessels and associated cells (neurovascular unit), effects mediated by vascular oxidative stress and inflammation. Injury to the neurovascular unit alters cerebral blood flow regulation, depletes vascular reserves, disrupts the blood-brain barrier, and reduces the brain's repair potential, effects that amplify the brain dysfunction and damage exerted by incident ischemia and coexisting neurodegeneration. Clinical-pathological studies support the notion that vascular lesions aggravate the deleterious effects of AD pathology by reducing the threshold for cognitive impairment and accelerating the pace of the dementia. In the absence of mechanism-based approaches to counteract cognitive dysfunction, targeting vascular risk factors and improving cerebrovascular health offers the opportunity to mitigate the impact of one of the most disabling human afflictions.

Biomarkers of endothelial cell activation serve as potential surrogate markers for drug-induced vascular injury

Drug-induced vascular injury (DIVI) is a nonclinical finding that often confounds the toxicological evaluation of investigational drugs, but there is an absence of qualified biomarkers that can be used to detect and monitor its appearance in animals and patients during drug development and clinical use. It is well known that endothelial cell (EC) activation plays a key role in the expression and evolution of DIVI, and the various immunological and inflammatory factors involved in its expression may serve as potential biomarker candidates. Activated ECs change their morphology and gene expression, generating endothelial adhesion molecules, pro-coagulant molecules, cytokines, chemokines, vasodilators, nitric oxide, and acute-phase reactants. This review provides a brief historical background of EC activation and the search for biomarkers of early EC activation for monitoring DIVI. At present, no biomarkers of EC activation have been qualified to predict DIVI in the nonclinical or clinical context, and a robust pathologic foundation for their use is still lacking. We propose three categories of EC activation biomarkers: recommended surrogate markers, potentially useful markers, and emerging candidate markers. This review alerts pharmaceutical companies, research institutions, and regulatory agencies to the continuing need for reliable biomarkers of EC activation in drug development.

Distribution of the Feline Calicivirus Receptor Junctional Adhesion Molecule A in Feline Tissues

Junctional adhesion molecule A (JAM-A) is an immunoglobulin superfamily protein that plays an important role in the assembly and maintenance of tight junctions and the establishment of epithelial cell polarity. The feline JAM-A (fJAM-A) is a functional receptor for feline calicivirus (FCV). Among natural diseases associated with FCV infection, isolates that cause oral vesicular disease are detected in epithelial cells; however, isolates that cause systemic disease are detected in multiple cell types. The distribution of an FCV receptor or receptors in feline tissues is relevant to viral pathogenesis in that it should reflect the wide latitude of clinical sequelae associated with FCV infection. The authors examined the expression of feline JAM-A in the cat by using confocal immunofluorescence localization on normal tissues, with special regard to tissue targets of naturally occurring FCV. As described in the human and the mouse, fJAM-A was widely distributed in feline tissues, where it localized at cell–cell junctions of epithelial and endothelial cells. fJAM-A was highly expressed on feline platelets, with lower levels of expression on feline peripheral blood leukocytes. Additionally, FCV infection of a feline epithelial cell monolayer causes redistribution of fJAM-A to the cytosol of infected cells. It is reasonable to propose that the spectrum of lesions caused by FCV reflects disruption of intercellular junctions that rely on fJAM-A function and tight junctional integrity.

Junctional adhesion molecule-C is a soluble mediator of angiogenesis

Junctional adhesion molecule-C (JAM-C) is an adhesion molecule expressed by endothelial cells (ECs) that plays a role in tight junction formation, leukocyte adhesion, and transendothelial migration. In the current study, we investigated whether JAM-C is found in soluble form and whether soluble JAM-C (sJAM-C) mediates angiogenesis. We found that JAM-C is present in soluble form in normal serum and elevated in rheumatoid arthritis (RA) serum. The concentration of sJAM-C is also elevated locally in RA synovial fluid compared with RA serum or osteoarthritis synovial fluid. sJAM-C was also present in the culture supernatant of human microvascular ECs (HMVECs) and immortalized human dermal microvascular ECs, and its concentration was increased following cytokine stimulation. In addition, sJAM-C cleavage from the cell surface was mediated in part by a disintegrin and metalloproteinases 10 and 17. In functional assays, sJAM-C was both chemotactic and chemokinetic for HMVECs and induced HMVEC tube formation on Matrigel in vitro. Neutralizing anti-JAM-C Abs inhibited RA synovial fluid-induced HMVEC chemotaxis and sJAM-C-induced HMVEC tube formation on Matrigel. sJAM-C also induced angiogenesis in vivo in the Matrigel plug and sponge granuloma models. Moreover, sJAM-C-mediated HMVEC chemotaxis was dependent on Src, p38, and PI3K. Our results show that JAM-C exists in soluble form and suggest that modulation of sJAM-C may provide a novel route for controlling pathological angiogenesis.

Tight junctions: is there a role in dermatology?

A variety of tight junction (TJ) proteins including claudins, occludin, tricellulin, zonula occludens-proteins and junctional adhesion molecules have been identified in complex localization patterns in mammalian epidermis. Their expression and/or localization is frequently altered in skin diseases including skin tumors. However, our understanding of the function(s) of TJ and TJ proteins in the skin is, even though rapidly increasing, still limited. This review summarizes our current knowledge of the involvement of TJ and TJ proteins in mammalian skin in functions ascribed to TJ in simple epithelia, such as barrier function, polarity, gene expression, proliferation, differentiation, and vesicle transport.

Regulation of endothelial permeability via paracellular and transcellular transport pathways

The endothelium functions as a semipermeable barrier regulating tissue fluid homeostasis and transmigration of leukocytes and providing essential nutrients across the vessel wall. Transport of plasma proteins and solutes across the endothelium involves two different routes: one transcellular, via caveolae-mediated vesicular transport, and the other paracellular, through interendothelial junctions. The permeability of the endothelial barrier is an exquisitely regulated process in the resting state and in response to extracellular stimuli and mediators. The focus of this review is to provide a comprehensive overview of molecular and signaling mechanisms regulating endothelial barrier permeability with emphasis on the cross-talk between paracellular and transcellular transport pathways.

The coxsackievirus-adenovirus receptor reveals complex homophilic and heterophilic interactions on neural cells

The coxsackievirus-adenovirus receptor (CAR) is a member of the Ig superfamily strongly expressed in the developing nervous system. Our histological investigations during development reveal an initial uniform distribution of CAR on all neural cells with a concentration on membranes that face the margins of the nervous system (e.g., the basal laminae and the ventricular side). At more advanced stages, CAR becomes downregulated and restricted to specific regions including areas rich in axonal and dendritic surfaces. To study the function of CAR on neural cells, we used the fiber knob of the adenovirus, extracellular CAR domains, blocking antibodies to CAR, as well as CAR-deficient neural cells. Blocking antibodies were found to inhibit neurite extension in retina organ and retinal explant cultures, whereas the application of the recombinant fiber knob of the adenovirus subtype Ad2 or extracellular CAR domains promoted neurite extension and adhesion to extracellular matrices. We observed a promiscuous interaction of CAR with extracellular matrix glycoproteins, which was deduced from analytical ultracentrifugation experiments, affinity chromatography, and adhesion assays. The membrane proximal Ig domain of CAR, termed D2, was found to bind to a fibronectin fragment, including the heparin-binding domain 2, which promotes neurite extension of wild type, but not of CAR-deficient neural cells. In contrast to heterophilic interactions, homophilic association of CAR involves both Ig domains, as was revealed by ultracentrifugation, chemical cross-linking, and adhesion studies. The results of these functional and binding studies are correlated to a U-shaped homodimer of the complete extracellular domains of CAR detected by x-ray crystallography.

Comprehensive analysis of lymph node stroma-expressed Ig superfamily members reveals redundant and nonredundant roles for ICAM-1, ICAM-2, and VCAM-1 in lymphocyte homing

Although it is well established that stromal intercellular adhesion molecule-1 (ICAM-1), ICAM-2, and vascular cell adhesion molecule-1 (VCAM-1) mediate lymphocyte recruitment into peripheral lymph nodes (PLNs), their precise contributions to the individual steps of the lymphocyte homing cascade are not known. Here, we provide in vivo evidence for a selective function for ICAM-1 > ICAM-2 > VCAM-1 in lymphocyte arrest within noninflamed PLN microvessels. Blocking all 3 CAMs completely inhibited lymphocyte adhesion within PLN high endothelial venules (HEVs). Post-arrest extravasation of T cells was a 3-step process, with optional ICAM-1-dependent intraluminal crawling followed by rapid ICAM-1- or ICAM-2-independent diapedesis and perivascular trapping. Parenchymal motility of lymphocytes was modestly reduced in the absence of ICAM-1, while ICAM-2 and alpha4-integrin ligands were not required for B-cell motility within follicles. Our findings highlight nonredundant functions for stromal Ig family CAMs in shear-resistant lymphocyte adhesion in steady-state HEVs, a unique role for ICAM-1 in intraluminal lymphocyte crawling but redundant roles for ICAM-1 and ICAM-2 in lymphocyte diapedesis and interstitial motility.

Molecular insights and therapeutic targets for blood-brain barrier disruption in ischemic stroke: critical role of matrix metalloproteinases and tissue-type plasminogen activator

Blood-brain barrier (BBB) disruption, mediated through matrix metalloproteinases (MMPs) and other mechanisms, is a critical event during ischemic stroke. Tissue plasminogen activator (tPA) is the only FDA-approved thrombolytic therapy for acute ischemic stroke, but the efficacy and safety of its therapeutic application are limited by narrow treatment time windows and side effects. Thus, there is a pressing need to develop combinational therapy that could offset tPA side effects and improve efficacy in clinical practice. Recent experimental studies indicate that tPA has previously unidentified functions in the brain beyond its well-established thrombolytic activity, which might contribute to tPA-related side effects through MMPs (mainly MMP-9) and several signaling pathways involved in LDL receptor-related protein (LRP), activated protein C (APC) and protease-activated receptor 1 (PAR-1), platelet-derived growth factor C (PDGF-C), and N-methyl-d-aspartate (NMDA) receptor. Therapeutic targeting of MMPs and/or tPA-related signaling pathways might offer promising new approaches to combination therapies for ischemic stroke. This review provides an overview of the relationship between structural components and function of the BBB/neurovascular unit with respect to ischemic stroke. We discuss how MMPs and tPA contribute to BBB disruption during ischemic stroke and highlight recent findings of molecular signaling pathways involved in neurotoxicity of tPA therapy.

Therapeutic targeting of chemokine interactions in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall that is characterized by a disturbed equilibrium of immune responses and lipid accumulation, leading to the development of plaques. The atherogenic influx of mononuclear cells is orchestrated by chemokines and their receptors. Studies using gene-deficient mice and antagonists based on peptides and small molecules have generated insight into targeting chemokine-receptor axes for treating atherosclerosis, which might complement lipid-lowering strategies and risk factor modulation. Combined inhibition of multiple chemokine axes could interfere with the contributions of chemokines to disease progression at specific cells, stages or sites. In addition, the recently characterized heterophilic interactions of chemokines might present a novel target for the treatment and prevention of inflammatory diseases such as atherosclerosis.

Challenges of stem cell therapy for spinal cord injury: human embryonic stem cells, endogenous neural stem cells, or induced pluripotent stem cells?

Spinal cord injury (SCI) causes myelopathy, damage to white matter, and myelinated fiber tracts that carry sensation and motor signals to and from the brain. The gray matter damage causes segmental losses of interneurons and motoneurons and restricts therapeutic options. Recent advances in stem cell biology, neural injury, and repair, and the progress toward development of neuroprotective and regenerative interventions are the basis for increased optimism. This review summarizes the pathophysiological mechanisms following SCI and compares human embryonic, adult neural, and the induced pluripotent stem cell-based therapeutic strategies for SCI.

JAM-A is a novel surface marker for NG2-Glia in the adult mouse brain

Background

Junctional adhesion molecule-A (JAM-A) is an adhesive protein expressed in various cell types. JAM-A localizes to the tight junctions between contacting endothelial and epithelial cells, where it contributes to cell-cell adhesion and to the control of paracellular permeability.

Results

So far, the expression pattern of JAM-A has not been described in detail for the different cell types of the adult brain. Here we show that a subset of proliferating cells in the adult mouse brain express JAM-A. We further clarify that these cells belong to the lineage of NG2-glia cells. Although these mitotic NG2-glia cells express JAM-A, the protein never shows a polarized subcellular distribution. Also non-mitotic NG2-glia cells express JAM-A in a non-polarized pattern on their surface.

Conclusions

Our data show that JAM-A is a novel surface marker for NG2-glia cells of the adult brain.

LFA-1 binding destabilizes the JAM-A homophilic interaction during leukocyte transmigration

Leukocyte transendothelial migration into inflamed areas is regulated by the integrity of endothelial cell junctions and is stabilized by adhesion molecules including junctional adhesion molecule-A (JAM-A). JAM-A has been shown to participate in homophilic interactions with itself and in heterophilic interactions with leukocyte function-associated antigen-1 (LFA-1) via its first and second immunoglobulin domains, respectively. Using competitive binding assays in conjunction with atomic force microscopy adhesion measurements, we provide compelling evidence that the second domain of JAM-A stabilizes the homophilic interaction because its deletion suppresses the dynamic strength of the JAM-A homophilic interaction. Moreover, binding of the LFA-1 inserted domain to the second domain of JAM-A reduces the dynamic strength of the JAM-A homophilic interaction to the level measured with the JAM-A domain 2 deletion mutant. This finding suggests that LFA-1 binding cancels the stabilizing effects of the second immunoglobulin domain of JAM-A. Finally, our atomic force microscopy measurements reveal that the interaction of JAM-A with LFA-1 is stronger than the JAM-A homophilic interaction. Taken together, these results suggest that LFA-1 binding to JAM-A destabilizes the JAM-A homophilic interaction. In turn, the greater strength of the LFA-1/JAM-A complex permits it to support the tension needed to disrupt the JAM-A homophilic interaction, thus allowing transendothelial migration to proceed.

Inactivation of junctional adhesion molecule-A enhances antitumoral immune response by promoting dendritic cell and T lymphocyte infiltration

Junctional adhesion molecule-A (JAM-A)-null dendritic cells (DCs) are more motile and effective than their wild-type counterpart in promoting contact hypersensitivity reaction. Here, we show that the growth and aggressiveness of pancreatic islet cell carcinoma induced by SV40 T antigen expression in beta cells (Rip1Tag2 mice) are significantly reduced in JAM-A-null mice. Because these tumor cells do not express JAM-A, we focused on changes in stroma reactivity. In the absence of JAM-A, tumors showed a small but significant reduction in angiogenesis and a marked increase in the immune reaction with enhanced infiltration of DCs (CD11c+ and MHC-II+) and CD4+ and CD8+ lymphocytes. In contrast, phagocyte number was not affected. DC capacity to produce cytokines was not significantly altered, but transmigration through JAM-A-null endothelial cells was increased as compared with JAM-A-positive endothelium. On adoptive transfer, JAM-A(-/-) DCs were recruited to tumors at slightly but significantly higher rate than JAM-A(+/+) DCs. Ablation of CD4+ and CD8+ cells with specific antibodies abrogated the inhibitory effect of JAM-A deletion on tumor growth and angiogenesis. These findings support the idea that, in the Rip1Tag2 tumor model, abrogation of JAM-A reduces cancer development by increasing antitumor immune response.

The regulation of leucocyte transendothelial migration by endothelial signalling events

Leucocytes use sophisticated mechanisms to cross the endothelium lining the vasculature. This is initiated by chemokine- and adhesion molecule-induced intracellular signalling that controls adhesion, spreading, and motility. At the same time, adherent leucocytes trigger the endothelium, manipulating the barrier to promote their transmigration into the underlying tissues. Over the past years, our insights in the associated signalling events within the endothelium have increased considerably, albeit the order of events, their crosstalk, and the consequences for endothelial cells and leucocytes are only partially resolved. Here, we briefly review endothelial signalling that is initiated at the apical endothelial membrane, where the first contact with the leucocytes takes place and signal transduction is induced. In addition, we discuss subsequent events at endothelial cell-cell junctions insofar as they have been linked to transendothelial migration. Finally, we briefly touch upon the modulation of endothelial signalling by infectious pathogens, since these have developed additional, elegant ways to manipulate the endothelium and transendothelial migration that may provide new, relevant insights into this process.

Mechanisms of action of estrogen receptors in vascular cells: relevance for menopause and aging

Estrogen exerts pleiotropic functions on the cardiovascular system through binding to estrogen receptors (ERs). Traditionally, ERs have been recognized as transcription factors regulating the expression of target genes. In the past decades, however, numerous studies have revealed rapid actions of estrogen in different systems, especially in non-reproductive tissues such as the cardiovascular system. At this level, estrogen triggers rapid vasodilatation, exerts anti-inflammatory effects, regulates vascular cell growth and migration, and confers protection to cardiomyocytes. These so-called 'extranuclear actions' do not require gene expression or protein synthesis and are independent of the nuclear localization of ERs. Indeed, some of these actions are elicited by ERs residing at or near the plasma membrane. Through complex interactions with membrane-associated signaling molecules such as ion channels, G proteins and the tyrosine kinase c-Src, liganded extranuclear ERs lead to the activation of downstream cascades such as mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-OH kinase (PI3K). These cascades are responsible for important cardiovascular actions of estrogen, for instance, the activation of nitric oxide synthesis or the remodeling of the endothelial actin cytoskeleton. Moreover, these cascades play crucial roles in regulating the expression of target proteins implicated in cell proliferation, apoptosis, differentiation, movement and homeostasis. Recent advancements in the characterization of the molecular basis of the extranuclear signaling of estrogen help us to understand the biological functions of estrogen and would be beneficial in elucidating current controversies on estrogen's clinical efficacy in the cardiovascular system.

Venular basement membranes ubiquitously express matrix protein low-expression regions: characterization in multiple tissues and remodeling during inflammation

The venular basement membrane plays a critical role in maintaining the integrity of blood vessels and through its dense and highly organized network of matrix proteins also acts as a formidable barrier to macromolecules and emigrating leukocytes. Leukocytes can however penetrate the venular basement membrane at sites of inflammation, though the associated in vivo mechanisms are poorly understood. Using whole mount immunostained tissues and confocal microscopy, we demonstrate that the venular basement membrane of multiple organs expresses regions of low matrix protein (laminin-511 and type IV collagen) deposition that have been termed low-expression regions (LERs). In the multiple tissues analyzed (eg, cremaster muscle, skin, mesenteric tissue), LERs were directly aligned with gaps between adjacent pericytes and were more prevalent in small venules. As predicted by their permissive nature, LERs acted as "gates" for transmigrating neutrophils in all inflammatory reactions investigated (elicited by leukotriene B(4) [LTB(4)], CXCL1, tumor necrosis factor [TNF]alpha, endotoxin, and ischemia/reperfusion [I/R] injury), and this response was associated with an enhancement of the size of laminin-511 and type IV collagen LERs. Transmigrated neutrophils stained positively for laminins but not type IV collagen, suggesting that different mechanisms exist in remodeling of different basement membrane networks. Collectively the findings provide further insight into characteristics of specialized regions within venular basement membranes that are preferentially used and remodeled by transmigrating neutrophils.

Recent developments and complexities in neutrophil transmigration

PURPOSE OF REVIEW

As the migration of neutrophils from blood to inflamed tissues is an essential component of innate immunity and a key contributing factor to the pathogenesis of inflammatory disorders, this aspect of leukocyte biology continues to be a highly dynamic field of research. This review summarizes recent findings in this area, focusing on the mechanisms that mediate neutrophil transmigration, an area where significant progress has been made.

RECENT FINDINGS

The topics to be covered will include responses that are prerequisite to neutrophil migration through venular walls, such as leukocyte luminal crawling and cellular and molecular changes in leukocytes and endothelial cells (e.g. formation of protrusions) that collectively support leukocyte transendothelial cell migration. Advances in both paracellular and transcellular neutrophil migration through endothelial cells will be discussed, addressing the associated roles and regulation of expression of endothelial cell luminal and junctional adhesion molecules. Beyond the endothelium, migration through the vascular pericyte coverage and basement membrane will be reviewed.

SUMMARY

The unquestionable role of neutrophils in the development and progression of inflammatory conditions suggests that a better understanding of the tissue-specific and stimulus-specific mechanisms that mediate this response may identify novel pathways that could be exploited for the development of more specific anti-inflammatory interventions.

Brief focal cerebral ischemia that simulates transient ischemic attacks in humans regulates gene expression in rat peripheral blood

Blood gene expression profiles of very brief (5 and 10 mins) focal ischemia that simulates transient ischemic attacks in humans were compared with ischemic stroke (120 mins focal ischemia), sham, and naïve controls. The number of significantly regulated genes after 5 and 10 mins of cerebral ischemia was 39 and 160, respectively (fold change >/=mid R:1.5mid R: and P<0.05). There were 103 genes common to brief focal ischemia and ischemic stroke. Ingenuity pathway analysis showed that genes regulated in the 5 mins group were mainly involved in small molecule biochemistry. Genes regulated in the 10 mins group were involved in cell death, development, growth, and proliferation. Such genes were also regulated in the ischemic stroke group. Genes common to ischemia were involved in the inflammatory response, immune response, and cell death-indicating that these pathways are a feature of focal ischemia, regardless of the duration. These results provide evidence that brief focal ischemia differentially regulates gene expression in the peripheral blood in a manner that could distinguish brief focal ischemia from ischemic stroke and controls in rats. We postulate that this will also occur in humans.

Ccl2 and Ccl3 Mediate Neutrophil Recruitment via Induction of Protein Synthesis and Generation of Lipid Mediators

Objective— Although the chemokines monocyte chemoattractant protein-1 (Ccl2/JE/MCP-1) and macrophage inflammatory protein-1α (Ccl3/MIP-1α) have recently been implicated in neutrophil migration, the underlying mechanisms remain largely unclear.

Methods and Results— Stimulation of the mouse cremaster muscle with Ccl2/JE/MCP-1 or Ccl3/MIP-1α induced a significant increase in numbers of firmly adherent and transmigrated leukocytes (>70% neutrophils) as observed by in vivo microscopy. This increase was significantly attenuated in mice receiving an inhibitor of RNA transcription (actinomycin D) or antagonists of platelet activating factor (PAF; BN 52021) and leukotrienes (MK-886; AA-861). In contrast, leukocyte responses elicited by PAF and leukotriene-B 4 (LTB 4 ) themselves were not affected by actinomycin D, BN 52021, MK-886, or AA-861. Conversely, PAF and LTB 4 , but not Ccl2/JE/MCP-1 and Ccl3/MIP-1α, directly activated neutrophils as indicated by shedding of CD62L and marked upregulation of CD11b. Moreover, Ccl2/JE/MCP-1- and Ccl3/MIP-1α-elicited leakage of fluorescein isothiocyanate dextran as well as collagen IV remodeling within the venular basement membrane were completely absent in neutrophil-depleted mice.

Conclusions— Ccl2/JE/MCP-1 and Ccl3/MIP-1α mediate firm adherence and (subsequent) transmigration of neutrophils via protein synthesis and secondary generation of leukotrienes and PAF, which in turn directly activate neutrophils. Thereby, neutrophils facilitate basement membrane remodeling and promote microvascular leakage.

Novel aspects in the regulation of the leukocyte adhesion cascade

Leukocyte recruitment plays a major role in the immune response to infectious pathogens and during inflammatory and autoimmune disorders. The process of leukocyte extravasation from the blood into the inflamed tissue requires a complex cascade of adhesive events between the leukocytes and the endothelium including leukocyte rolling, adhesion and transendothelial migration. Leukocyte-endothelial interactions are mediated by tightly regulated binding interactions between adhesion receptors on both cells. In this regard, leukocyte adhesion onto the endothelium is governed by leukocyte integrins and their endothelial counter-receptors of the immunoglobulin superfamily. The present review will focus on novel aspects with respect to the modulation of the leukocyte adhesion cascade.

Vascular integrity mediated by vascular endothelial cadherin and regulated by sphingosine 1-phosphate and angiopoietin-1

Development of blood vessels is coordinated by angiogenesis and stabilization of vascular endothelial cells (ECs). The vascular network is established during embryogenesis to supply oxygen and nutrients to the tissues and organs. However, after cardiac or peripheral ischemia is caused by occlusion of the vessels, new vessels must be formed to rescue the ischemic tissues. Many angiogenic growth factors and chemokines are produced in the ischemic tissue to induce angiogenic sprouting of preexisting vessels. Branched vessels must be again restabilized to form mature vessels that deliver blood to the tissues. To this end, vascular EC-cell adhesion is tightly regulated by cell-cell adhesion molecules and extracellular stimuli that activate G protein-coupled receptors and receptor tyrosine kinases exclusively expressed on vascular ECs. This review spotlights the recent studies of vascular endothelial cadherin and of sphingosine 1-phosphate signaling and angiopoietin-Tie signaling.

Mechanisms of transendothelial migration of leukocytes

A great deal of progress has been made recently in understanding the molecules and mechanisms that regulate transendothelial migration of leukocytes, or diapedesis, a critical step in the inflammatory response. This review focuses mainly on the active role of the endothelial cell in this process as it occurs at endothelial cell borders. It discusses some of the many molecules that have been reported to play a role in transendothelial migration and asks why so many molecules seem to be involved. The concept is emerging that diapedesis itself can be dissected into sequential steps controlled by specific molecule(s) at the endothelial cell border. Several mechanisms have been shown to play a critical role in transendothelial migration including signals derived from clustering of apically disposed intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, disruption or loosening of adherens junctions, and targeted recycling of platelet/endothelial cell adhesion molecule and other molecules from the recently described lateral border recycling compartment. A hypothesis that integrates the various known mechanisms is proposed.

Disruption of tight junctions by cellulose sulfate facilitates HIV infection: model of microbicide safety

BACKGROUND

The lack of biomarkers that are predictive of safety is a critical gap in the development of microbicides. The present experiments were designed to evaluate the predictive value of in vitro models of microbicide safety.

METHODS

Changes in the epithelial barrier were evaluated by measuring transepithelial electrical resistance (TER) after exposure of human epithelial cells to candidate microbicides in a dual-chamber system. The significance of observed changes was addressed by challenging cultures with human immunodeficiency virus (HIV) and measuring the ability of virus to cross the epithelium and infect target T cells cultured in the lower chamber.

RESULTS

Exposure to nonoxynol-9 (N-9) or cellulose sulfate (CS), but not 9-[2-(phosphonomethoxy)propyl]adenine (also referred to as tenofovir) or PRO2000, resulted in a rapid and sustained reduction in TER and a marked increase in HIV infection of T cells cultured in the lower chamber. Moreover, CS triggered nuclear factor kappaB activation in peripheral blood mononuclear cells and increased HIV replication in chronically infected U1 cells.

CONCLUSIONS

Epithelial barrier disruption and enhanced viral replication may have contributed to the increased risk of HIV acquisition observed in phase 3 trials of N-9 and CS. Expansion of in vitro safety testing to include these models would provide a more stringent preclinical assessment of microbicide safety and may prove to be more predictive of clinical outcomes.

Neutrophil granule proteins tune monocytic cell function

Polymorphonuclear leukocytes (PMNs) release the contents of granules during their migration to inflammatory sites. On liberation from the first leukocyte to enter injured tissue, the granule proteins play a central role in the early inflammatory response. In particular, mononuclear phagocytes interact intimately with PMNs and their secretion products. PMN granule proteins enhance the adhesion of monocytes to the endothelium and stimulate subsequent extravasation of inflammatory monocytes. At the site of inflammation, PMN granule proteins activate macrophages to produce and release cytokines and to phagocytose IgG-opsonized bacteria. Furthermore, by direct cell-cell contacts, PMNs activate monocyte-derived dendritic cells, thereby enhancing antigen presentation. Efforts in this field might lead to the development of drugs for specific modulation of innate immune functions.

Alteration of tight junction proteins is an early event in psoriasis: putative involvement of proinflammatory cytokines

Psoriasis is an inflammatory skin disease characterized by hyperproliferation of keratinocytes, impaired barrier function, and pronounced infiltration of inflammatory cells. Tight junctions (TJs) are cell-cell junctions that form paracellular barriers for solutes and inflammatory cells. Altered localization of TJ proteins in the epidermis was described in plaque-type psoriasis. Here we show that localization of TJ proteins is already altered in early-stage psoriasis. Occludin, ZO-1, and claudin-4 are found in more layers than in normal epidermis, and claudin-1 and -7 are down-regulated in the basal and in the uppermost layers. In plaque-type psoriasis, the staining patterns of occludin and ZO-1 do not change, whereas the claudins are further down-regulated. Near transmigrating granulocytes, all TJ proteins except for junctional adhesion molecule-A are down-regulated. Treatment of cultured keratinocytes with interleukin-1beta and tumor necrosis factor-alpha, which are present at elevated levels in psoriatic skin, results in an increase of transepithelial resistance at early time points and a decrease at later time points. Injection of interleukin-1beta into an ex vivo skin model leads to an up-regulation of occludin and ZO-1, resembling TJ protein alteration in early psoriasis. Our results show for the first time that alteration of TJ proteins is an early event in psoriasis and is not the consequence of the more profound changes found in plaque-type psoriasis. Our data indicate that cytokines are involved in alterations of TJ proteins observed in psoriasis.

Molecular basis of leukocyte-endothelium interactions during the inflammatory response

The process of leukocyte extravasation, a critical step in the inflammatory response, involves the migration of leukocytes from the bloodstream towards target tissues, where they exert their effector function. Leukocyte extravasation is orchestrated by the combined action of cellular adhesion receptors and chemotactic factors, and involves radical morphological changes in both leukocytes and endothelial cells. Thus, it constitutes an active process for both cell types and promotes the rapid and efficient influx of leukocytes to inflammatory foci without compromising the integrity of the endothelial barrier. This article provides a review of leukocyte extravasation from both molecular and mechanical points of view, with a particular emphasis on the most recent findings on the topic. It includes a description of newly revealed steps in the adhesion cascade, such as slow rolling motion, intraluminal crawling and alternative pathways for transcellular migration, and discusses the functional role of novel adhesion receptors, the spatiotemporal organization of receptors at the plasma membrane and the signaling pathways that control different phases of the extravasation process.

The role of JAM-A in inflammatory bowel disease: unrevealing the ties that bind

Tight junctions (TJ) are junctional proteins whose function is to maintain an intact intestinal epithelial barrier and regulate the paracellular movement of water and solutes. Altered TJ structure and epithelial permeability are observed in inflammatory bowel disease and seem to have an important role in the pathogenesis of these diseases. Junctional adhesion molecule-A (JAM-A) is a protein expressed at tight junctions of epithelial and endothelial cells, as well as on circulating leukocytes. Its function at tight junctions appears to be crucial as an extracellular adhesive molecule in the direct regulation of intestinal barrier function. This review focuses on the role of JAM-A in controlling mucosal homeostasis by regulating the integrity and permeability of epithelial barrier function.

Unfolding individual als5p adhesion proteins on live cells

Elucidating the molecular mechanisms behind the strength and mechanics of cell adhesion proteins is of central importance in cell biology and offers exciting avenues for the identification of potential drug targets. Here we use single-molecule force spectroscopy to investigate the adhesive and mechanical properties of the widely expressed Als5p cell adhesion protein from the opportunistic pathogen Candida albicans . We show that the forces required to unfold individual tandem repeats of the protein are in the 150-250 pN range, both on isolated molecules and on live cells. We also find that the unfolding probability increases with the number of tandem repeats and correlates with the level of cell adherence. We suggest that the modular and flexible nature of Als5p conveys both strength and toughness to the protein, making it ideally suited for cell adhesion. The single-molecule measurements presented here open new avenues for understanding the mechanical properties of adhesion molecules from mammalian and microbial cells and may help us to elucidate their potential implications in diseases such as inflammation, cancer, and infection.

Acquired immunodeficiency syndrome and the blood-brain barrier

The blood-brain barrier (BBB) plays a critical role in normal physiology of the central nervous system by regulating what reaches the brain from the periphery. The BBB also plays a major role in neurologic disease including neuropathologic sequelae associated with infection by human immunodeficiency virus (HIV) in humans and the closely related simian immunodeficiency virus (SIV) in macaques. In this review, we provide an overview of the function, structure, and components of the BBB, followed by a more detailed discussion of the subcellular structures and regulation of the tight junction. We then discuss the ways in which HIV/SIV affects the BBB, largely through infection of monocytes/macrophages, and how infected macrophages crossing the BBB ultimately results in breakdown of the barrier.

Structural determinants of Junctional Adhesion Molecule A (JAM-A) function and mechanisms of intracellular signaling

Junctional Adhesion Molecule A (JAM-A) is a multifunctional cell surface protein that has multiple evolutionarily conserved structural features. There is now conclusive evidence that discrete structural elements on JAM-A mediate intracellular signaling events that alter cell migration and paracellular permeability. Specifically, self-dimerization between extracellular Ig-like loops and close apposition of PDZ-dependent, JAM-A-associated intracellular scaffold proteins such as Afadin and guanine-nucleotide exchange factors mediate activation of Rap1 and modulation of epithelial cell migration by effects on beta1 integrin. While the same JAM-A structural features also modulate migration of other cell types and paracellular permeability in epithelia/endothelia, additional signaling proteins/mechanisms are probably involved. Recent insights into JAM-A outside-in signaling events that regulate these cellular functions are discussed.

Junctional adhesion molecule-C mediates leukocyte infiltration in response to ischemia reperfusion injury

OBJECTIVE

Junctional adhesion molecule-C (JAM-C) is an adhesion molecule that has multiple roles in inflammation and vascular biology, but many aspects of its functions under pathological conditions are unknown. Here we investigated the role of JAM-C in leukocyte migration in response to ischemia reperfusion (I/R) injury.

METHODS AND RESULTS

Pretreatment of mice with soluble JAM-C (sJAM-C), used as a pharmacological blocker of JAM-C-mediated reactions, significantly suppressed leukocyte migration in models of kidney and cremaster muscle I/R injury (39 and 51% inhibition, respectively). Furthermore, in the cremaster muscle model (studied by intravital microscopy), both leukocyte adhesion and transmigration were suppressed in JAM-C-deficient mice (JAM-C(-/-)) and enhanced in mice overexpressing JAM-C in their endothelial cells (ECs). Analysis of JAM-C subcellular expression by immunoelectron microscopy indicated that in I/R-injured tissues, EC JAM-C was redistributed from cytoplasmic vesicles and EC junctional sites to nonjunctional plasma membranes, a response that may account for the role of JAM-C in both leukocyte adhesion and transmigration under conditions of I/R injury.

CONCLUSIONS

The findings demonstrate a role for EC JAM-C in mediating leukocyte adhesion and transmigration in response to I/R injury and indicate the existence of a novel regulatory mechanism for redistribution and hence function of EC JAM-C in vivo.