Carbohydrate synthesis inhibitors decrease interleukin 1-stimulated lymphocyte binding to endothelial cells

The significant role of the Golgi apparatus in cardiovascular diseases

The Golgi apparatus (GA) is a ribbon-like system of stacks which consist of multiple closely apposed flattened cisternae and vesicles usually localized in the juxta-nuclear area. As for the biological functions, the GA plays a major role in protein biosynthesis, post-translational modification, and sorting protein from ER to plasma membrane and other destinations. Structural changes and functional disorder of the GA is associated with various diseases. Moreover, increasing evidence revealed that swelling, poor development, and other morphological alterations of the GA are linked to cardiovascular diseases such as heart failure (HF), arrhythmia, and dilated cardiomyopathy. Furthermore, dysfunction of the GA is also related to cardiovascular diseases since the GA is extremely responsible for transport, glycosylation, biosynthesis, and subcellular distribution of cardiovascular proteins. This review gives a brief overview of the intricate relationship between the GA and cardiovascular diseases. In addition, we provide a further prospective that the GA may provide diagnosis reference for cardiovascular diseases, and changes in the ultrastructure and morphology of the GA such as swelling, poor development, and fragmentation may serve as a reliable index for cardiovascular diseases.

Immunosuppressive drugs affect high-mannose/hybrid N-glycans on human allostimulated leukocytes

N-glycosylation plays an important role in the majority of physiological and pathological processes occurring in the immune system. Alteration of the type and abundance of glycans is an element of lymphocyte differentiation; it is also common in the development of immune-mediated inflammatory diseases. The N-glycosylation process is very sensitive to different environmental agents, among them the pharmacological environment of immunosuppressive drugs. Some results show that high-mannose oligosaccharides have the ability to suppress different stages of the immune response. We evaluated the effects of cyclosporin A (CsA) and rapamycin (Rapa) on high-mannose/hybrid-type glycosylation in human leukocytes activated in a two-way mixed leukocyte reaction (MLR). CsA significantly reduced the number of leukocytes covered by high-mannose/hybrid N-glycans, and the synergistic action of CsA and Rapa led to an increase of these structures on the remaining leukocytes. This is the first study indicating that β1 and β3 integrins bearing high-mannose/hybrid structures are affected by Rapa and CsA. Rapa taken separately and together with CsA changed the expression of β1 and β3 integrins and, by regulating the protein amount, increased the oligomannose/hybrid-type N-glycosylation on the leukocyte surface. We suggest that the changes in the glycosylation profile of leukocytes may promote the development of tolerance in transplantation.

Endothelial heterogeneity and adhesion molecules N-glycosylation: implications in leukocyte trafficking in inflammation

Inflammation is a major contributing element to a host of diseases with the interaction between leukocytes and the endothelium being key in this process. Much is understood about the nature of the adhesion molecule proteins expressed on any given leukocyte and endothelial cell that modulates adhesive interactions. Although it is appreciated that these proteins are heavily glycosylated, relatively little is known about the roles of these posttranslational modifications and whether they are regulated, and if so how during inflammation. Herein, we suggest that a paucity in this understanding is one major reason for the lack of successful therapies to date for modulating leukocyte-endothelial interactions in human inflammatory disease and discuss developing paradigms of (i) how endothelial adhesion molecule glycosylation (with a focus on N-glycosylation) maybe a critical element in understanding endothelial heterogeneity between different vascular beds and species, (ii) how adhesion molecule N-glycosylation may be under distinct, and as yet, unknown modes of regulation during inflammatory stress to affect the inflammatory response in a vascular bed- and disease-specific manner (analogous to a "zip code" for inflammation) and finally (iii) to underscore the concept that a fuller appreciation of the role of adhesion molecule glycoforms is needed to provide foundations for disease and tissue-specific targeting of inflammation.

Endothelial surface N-glycans mediate monocyte adhesion and are targets for anti-inflammatory effects of peroxisome proliferator-activated receptor γ ligands

Endothelial-monocyte interactions are regulated by adhesion molecules and key in the development of vascular inflammatory disease. Peroxisome proliferator-activated receptor (PPAR) γ activation in endothelial cells is recognized to mediate anti-inflammatory effects that inhibit monocyte rolling and adhesion. Herein, evidence is provided for a novel mechanism for the anti-inflammatory effects of PPARγ ligand action that involves inhibition of proinflammatory cytokine-dependent up-regulation of endothelial N-glycans. TNFα treatment of human umbilical vein endothelial cells increased surface expression of high mannose/hybrid N-glycans. A role for these sugars in mediating THP-1 or primary human monocyte rolling and adhesion was indicated by competition studies in which addition of α-methylmannose, but not α-methylglucose, inhibited monocyte rolling and adhesion during flow, but not under static conditions. This result supports the notion that adhesion molecules provide scaffolds for sugar epitopes to mediate adhesion with cognate receptors. A panel of structurally distinct PPARγ agonists all decreased TNFα-dependent expression of endothelial high mannose/hybrid N-glycans. Using rosiglitazone as a model PPARγ agonist, which decreased TNFα-induced high mannose N-glycan expression, we demonstrate a role for these carbohydrate residues in THP-1 rolling and adhesion that is independent of endothelial surface adhesion molecule expression (ICAM-1 and E-selectin). Data from N-glycan processing gene arrays identified α-mannosidases (MAN1A2 and MAN1C1) as targets for down-regulation by TNFα, which was reversed by rosiglitazone, a result consistent with altered high mannose/hybrid N-glycan epitopes. Taken together we propose a novel anti-inflammatory mechanism of endothelial PPARγ activation that involves targeting protein post-translational modification of adhesion molecules, specifically N-glycosylation.

Alpha-1,2-mannosidase and hence N-glycosylation are required for regulatory T cell migration and allograft tolerance in mice

Background

Specific immunological unresponsiveness to alloantigens can be induced in vivo by treating mice with a donor alloantigen in combination with a non-depleting anti-CD4 antibody. This tolerance induction protocol enriches for alloantigen reactive regulatory T cells (Treg). We previously demonstrated that alpha-1,2-mannosidase, an enzyme involved in the synthesis and processing of N-linked glycoproteins, is highly expressed in tolerant mice, in both graft infiltrating leukocytes and peripheral blood lymphocytes.

Principal Findings

In this study we have identified that alpha-1,2-mannosidase expression increases in CD25⁺CD4⁺ Treg when they encounter alloantigen in vivo. When alpha-1,2-mannosidase enzyme activity was blocked, Treg retained their capacity to suppress T cell proliferation in vitro but were unable to bind to physiologically relevant ligands in vitro. Further in vivo analysis demonstrated that blocking alpha-1,2-mannosidase in Treg resulted in the migration of significantly lower numbers to the peripheral lymph nodes in skin grafted mice following adoptive transfer, where they were less able to inhibit the proliferation of naïve T cells responding to donor alloantigen and hence unable prevent allograft rejection in vivo.

Significance

Taken together, our results suggest that activation of alloantigen reactive Treg results in increased alpha-1,2-mannosidase expression and altered N-glycosylation of cell surface proteins. In our experimental system, altered N-glycosylation is not essential for intrinsic Treg suppressive capacity, but is essential in vivo as it facilitates Treg migration to sites where they can regulate immune priming. Migration of Treg is central to their role in regulating in vivo immune responses and may require specific changes in N-glycosylation upon antigen encounter.

Castanospermine, an oligosaccharide processing inhibitor, reduces membrane expression of adhesion molecules and prolongs heart allograft survival in rats

The inhibition of intracellular oligosaccharide processing is a new approach to immunosuppression in allotransplantation. The net effect of such inhibition is reduction in the membrane expression of certain glycoproteins. Hence cell-cell interaction in allorejection may be impaired in the presence of glycoprotein processing inhibitors because the expression of key ligand-receptor pairs of N-linked glycoproteins including adhesion molecules is inhibited. The aims of this study were to measure the immunosuppressive ability of castanospermine (CAST) in a rat heart allograft model, to measure its effect on membrane expression of adhesion molecules (LFA-1 alpha, LFA-1 beta, ICAM-1), class I and class II MHC antigens and on other T cell associated molecules (CD4, CD8, CD39, CD45, W3/13), to test its tolerogenic potential and its toxicity. Membrane expression of these molecules was measured by flow cytometry for single cells and by immunoperoxidase staining for the allograft. In grafted rats CAST significantly reduced the expression of LFA-1 alpha on lymphoid cells in the thymus, lymph node, spleen and heart allografts. ICAM-1 expression on endothelial cells of the allograft vasculature, class I and class II MHC expression on lymphoid cells in the thymus, class II MHC expression on lymphoid cells in the allograft; and CD4, CD8, CD45 and W3/13 expression on lymphoid cells in some organs. By contrast, in non-grafted rats CAST significantly upregulated expression of class I MHC and CD45 in the thymus, lymph node and spleen, ICAM-1 and CD4 on lymphoid cells in the spleen, but reduced expression of LFA-1 alpha on lymphoid cells in the thymus. It also prolonged rat heart allograft survival in a dose-dependent manner and with limited testing was relatively non-toxic. In conclusion, CAST is an immunosuppressive molecule which may work by downregulation of the ligand-receptor adhesion molecule pair, LFA-1 alpha-ICAM-1 although subtle downregulation of class I and II MHC, CD4 and CD8 molecules could also contribute to its immunosuppressive activity. Hence, both lymphocyte-endothelial cell binding and lymphocyte activation may be inhibited by CAST. This work suggests that CAST may hold significant potential as a transplant immunosuppressant probably as an adjuvant agent to inhibitors of interleukin 2 secretion.

Variations in the expression of cell-adhesion molecules on liver-associated lymphocytes and peripheral-blood lymphocytes in patients with and without liver metastasis

We evaluated the expression of the cell-adhesion molecules (CAM) that might be involved in liver-associated lymphocyte (LAL) contacts with other sinusoidal cells and/or be responsible for natural-killer(NK)- and lymphokine-activated killer(LAK) activity in patients with liver metastasis. The LAL population was isolated by sinusoidal high-pressure lavage from partial hepatectomies obtained from patients operated for metastases (n = 13) and benign liver tumors (n = 9). Surface expression of the beta-2-integrin chains (CD11a, CD11b, CD11c and CD18), and the beta-I-integrin chains (CD49b, CD49d, CD49f and CD29), as well as that of members of the immunoglobulin superfamily (CD2, CD54, CD56 and CD58), were analyzed by one- or two-color flow cytometry. Quantitative and qualitative differences were observed in both groups of patients in the expression of CAM between LAL and peripheral blood lymphocytes (PBL). LAL were characterized by an increase in the percentage of CD11b-, CD49b-, CD49d-, CD54-, CD56- and CD58-positive cells in comparison with PBL. Fluorescence values for CD2, CD11a, CD18 and CD56 were higher in LAL than in PBL. Moreover, the population expressing these antigens of differentiation presented a bimodal distribution (dim and bright): in LAL, as opposed to PBL, the percentage of cells with a bright phenotype was greater than of those with a dim one. The increase in CAM expression on LAL could be due to the influence of the liver sinusoidal micro-environment. Results were more unexpected for the comparison between benign and malignant tumors. No difference was found in CAM expression on LAL between these 2 categories. Consequently, it cannot be this factor that explains the decrease in LAK activity of LAL in patients with metastasis.

Cyclohexylamine inhibits the adhesion of lymphocytic cells to human syncytiotrophoblast

We have previously shown that lymphocytic cells adhere to cultured syncytiotrophoblast and that this may be important in the lymphocyte-mediated infection of trophoblast with the human immunodeficiency virus (HIV). During the course of studies aimed at investigating the role of cell surface carbohydrates in adhesion, it was discovered that a contaminant of commercial fucose-1-phosphate, dicyclohexylamine, inhibited MOLT-trophoblast adhesion. Dicyclohexylamine and the related compounds, cyclohexylamine and hexylamine, inhibited adhesion in a dose-responsive manner with half-maximal inhibition seen at about 4 mM. While the pressor effects of cyclohexylamine, the principal metabolite of cyclamate, are well known, this is the first report of an effect of this and related compounds on cell adhesion activity. The inhibitory effect was reversible and, at concentrations less than 25 mM, did not result in loss of cell viability. Several possible mechanisms of action of cyclohexylamine were examined in an attempt to explain the effect on adhesion. No evidence was found to suggest that the effects of cyclohexylamine were due to inhibition of polyamine synthesis, increase in intracellular Ca2+ concentration or to a lysosomotropic effect. The concentrations of cyclohexylamine used are within the range of plasma concentrations attainable in humans, raising the possibility that the in vitro effects described here may also occur in vivo. The results also suggest that caution should be used in the interpretation of results obtained from experiments where cell adhesion is blocked using exogenous monosaccharides that are in the form of dicyclohexylammonium salts. Appropriate controls must be included or, if possible, sodium, potassium or barium salts should be chosen.

Effects of the anti-inflammatory compounds castanospermine, mannose-6-phosphate and fucoidan on allograft rejection and elicited peritoneal exudates

The glycoprotein processing inhibitor castanospermine (CS) and the monosaccharide mannose-6-phosphate (M6P), as well as some sulfated polysaccharides (SPS), have been shown to inhibit inflammation in rat models of experimental autoimmune encephalomyelitis and adjuvant-induced arthritis. Here, the anti-inflammatory effects of these agents have been further explored in murine models of allograft rejection and elicitation of peritoneal exudates. CS, M6P and the SPS, fucoidan, partially inhibited rejection of permanently accepted thyroid allografts induced by the i.p. injection of donor strain (H-2d) spleen cells with a reduction in leucocyte infiltration of 25-36%. However none of these agents reduced the more extensive leucocyte infiltration induced by the i.p. injection of P815 (H-2d) unless recipient mice were pretreated with the immunosuppressant, cyclosporin A (CsA). Elicitation of peritoneal exudates by thioglycollate was inhibited by CS, M6P and fucoidan with sustained leucopenia being induced by CS. In contrast, CS and fucoidan, but not M6P, inhibited antigen-elicited peritoneal exudates. These results suggest that CS, M6P and the SPS fucoidan exhibit subtle differences in their anti-inflammatory activity but probably inhibit inflammation at the level of leucocyte extravasation.

Expression of six protein kinase C isotypes in endothelial cells

Protein kinase C (PKC) family is an important regulatory element in signal transduction, cellular regulation and tumor promotion. The classical PKC isotypes (alpha, beta and gamma) are Ca(2+)-dependent and can be activated by diacylglycerol. The novel isotypes, PKC delta, PKC epsilon, PKC eta (L) and PKC theta, are Ca(2+)-independent, whereas the two atypical PKCs (zeta and lambda) lack the Ca(2+)-binding region and are not activated by diacylglycerol. Here we show that cultured human endothelial cell line EA.hy926 as well as freshly isolated human umbilical vein endothelial cells express members of all PKC subfamilies. No traces of PKC gamma or delta were detected in endothelial cells. On the contrary the classical PKCs (alpha and beta), the novel PKC epsilon, as well as the atypical PKC zeta are present at the mRNA level in human endothelial cells and the corresponding proteins are also detected by immunoblotting.

Distribution of saccharides in pig lymph-node high-endothelial venules and associated lymphocytes visualized using fluorescent lectins and confocal microscopy

The distribution of saccharides in pig lymph nodes, particularly on high-endothelial venule (HEV) endothelium and on lymphocytes in these vessels, was studied by examining the binding of fluorescent conjugates of 18 different lectins. Eight of the lectins, particularly with glycan specificity restricted to mannose and polyacetyllactosamine determinants, were found to bind with a high affinity to these structures. Competitive inhibition experiments revealed that polylactosamine-containing glycans were present on endothelia and lymphocytes using lectins from Lycopersicon esculentum and Solanum tuberosum, the latter lectin reacting with lymphocytes only when apparently adherent to the luminal endothelium. The The absence on pig endothelium of the Ulex europaeus binding, shown by human endothelia due to the presence of certain fucose epitopes, was confirmed. Pig lymph-node endothelium, however, bound the fucose-specific lectin of Tetragonolobus purpureas, indicating the presence of fucose on pig endothelia in a different conformation to that seen on human endothelia. The results suggested that pig lymph-node HEV endothelium expressed a core fucosylated tri- or tetra-antennary complex glycan with polylactosamine extensions and expressing an Ley determinant.

Leucocyte endothelial cell adhesion: a study comparing human umbilical vein endothelial cells and the endothelial cell line EA-hy-926

EA-hy-926 is a cell line produced by hybridizing human umbilical vein endothelial cells (HUVEC) and the epithelial cell line A549. To establish whether EA-hy-926 could be used as a model for endothelial cells (EC) in leucocyte-EC adhesion interactions, the effect of interleukin-4 (IL-4), tumour necrosis factor (TNF) or interferon-gamma (IFN) stimulation on their adhesiveness and expression of E-selectin, vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) was compared with that of HUVEC and A549. Although HUVEC exhibited increased adhesiveness and adhesion molecule expression with IL-4, TNF or IFN, EA-hy-926 exhibited these responses only with TNF. CD11/CD18-dependent binding accounted for a significant component of basal binding to HUVEC and EA-hy-926, but did not account for the increased binding of T cells, JY, J6, ICH-BJ or ICH-KM cell lines to TNF-stimulated monolayers. At least part of the CD11/CD18-independent adhesion was attributable to VCAM-1 induction on HUVEC and EA-hy-926. TNF-stimulation also induced E-selectin expression on EA-hy-926 and HUVEC and an accompanying increase in neutrophil (PMN) binding. The EA-hy-926 cells used in this study, therefore, showed responses similar to HUVEC when stimulated with TNF but not when stimulated with IL-4 or IFN.

Adhesion of human lymphoid cell lines to immobilized carbohydrates and to bone-marrow stromal cell layers by surface sugar receptors

Cell-surface sugar receptors may participate in interactions of lymphoid cells that influence their adhesive properties and proliferation. Their expression on cells of the pre-B line BLIN-I, the B-lymphoblastoid line Croco II, the myeloma line RPMI 8226 and the T-lymphoblastoid line CCRF-CEM was monitored with a panel of 14 types of chemically glycosylated E. coli beta-galactosidase at a non-saturating ligand concentration. Quantitative differences were determined for the capacity of the different cell types to bind constituents of the carbohydrate part of glycoconjugates. They were corroborated by analyses of binding for lactose-, beta-N-acetylgalactosamine-, beta-N-acetylglucosamine- and fucose-exposing neoglycoenzymes up to saturation levels. Values of dissociation constants of the tetrameric enzyme were in the range of 3-300 nM. Several types of sugar receptor led to carbohydrate-inhibitable adhesion of cells to 6 types of nitrocellulose-immobilized neoglycoprotein, their effectiveness being most obvious for the myeloma cells. Analyses of the carbohydrate-ligand-mediated adhesion of the other cell types revealed a comparatively decreased response. Only a few carbohydrates among the 7 types tested were effective in reducing cell adhesion to a far more complex ligand-bearing matrix than immobilized neoglycoproteins, namely bone-marrow stromal cell layers: sialic acid and N-acetylgalactosamine for B-lymphoblastoid cells and rhamnose for pre-B cells. These cellular interactions may encompass sugar receptors on the stromal cells and other types of molecular recognition in addition to the detected activities on the lymphoid cells.

High mannose type N-linked oligosaccharides on endothelial cells may influence beta 2 integrin mediated neutrophil adherence in vitro

We report herein on the role of N-linked oligosaccharide processing of endothelial cell surface proteins on the adhesion of neutrophils. Monolayers of human umbilical vein endothelial cells were treated for 24 h with deoxymannojirimycin (DMJ), an inhibitor of golgi mannosidase I, which results in changes in glycoprotein processing, and then incubated with neutrophils to examine their ability to adhere to the treated endothelial cells. Treatment with DMJ, which leads to accumulation of high mannose type oligosaccharides, resulted in a twofold increase in adherence of phorbol ester (PMA) activated neutrophils compared to attachment to untreated endothelial cells. This adherence was likely mediated by the beta 2 integrin, Mac-1, and could be specifically inhibited with monoclonal antibodies to ICAM-1 and to the integrin beta 2 subunit. Similarly, IL-1 treatment resulted in a beta 2 integrin mediated increase in neutrophil adherence to the DMJ treated endothelial cells in a dose dependent manner. However, the IL-1 induced adherence was not significantly inhibited by the anti-ICM-1 antibody, thus, suggesting the presence of other inducible components on the endothelial cell surface. Our results demonstrate that alterations in glycosylation of N-linked oligosaccharides, resulting in the synthesis of high mannose type sugars on molecules that may interact with the beta 2 integrins, leads to an increased adherence of PMA activated neutrophils to endothelial cells.

Inhibition of adjuvant arthritis in the rat by phosphosugars and the alpha-glucosidase inhibitor castanospermine

The development of joint inflammation of adoptively transferred arthritis in rats was inhibited by treatment with the simple sugar mannose-6-phosphate or the alkaloid inhibitor of alpha-glucosidase, castanospermine. Mannose-6-phosphate was effective at a dose of 25 mg/kg per day delivered via mini-osmotic pumps implanted either subcutaneously or intraperitoneally. Castanospermine was given orally in the drinking water and rats ingested on average 60-65 mg/kg per day. Histological examination of tissue from treated rats revealed greatly reduced inflammatory infiltrates into the synovium and surrounding tissue. Castanospermine not only inhibited the development of arthritis but also inhibited the progression of the disease when treatment was commenced after the onset of symptoms. Possible mechanism(s) of action of these compounds could be their ability to inhibit the passage of leucocytes through vascular subendothelial basement membranes by inhibiting the function or expression of leucocyte cell surface-bound enzymes that are essential for such migration. Castanospermine could also inhibit inflammation through its ability to prevent the expression of adhesion molecules, which may be necessary for the capture and retention of leucocytes in the inflamed tissue.

Markers of the metastatic phenotype in prostate cancer

Metastatic malignant disease is the single most common cause of treatment failure and subsequent mortality of most human malignancies, including prostate cancer. Presently, cells expressing the metastatic phenotype cannot be identified within a primary tumor population. Hence, accurate assessment of the likely behavior of an individual primary malignancy cannot be made at the time of diagnosis. The studies now reported have been aimed at identifying some of the features that may be associated with the metastatic phenotype of prostatic cancer. Insight into those factors that may be involved in prostate cancer metastasis has been gained from a variety of experimental approaches as well as study of intact human prostate cancers.

Effect of inhibitors of N-linked oligosaccharide processing on the high-affinity transport of D-aspartate by C6 glioma cells

The effect of several inhibitors of oligosaccharide-processing on the high-affinity transport of D-aspartate was investigated in C6 glioma cells. Swainsonine, an inhibitor of mannosidase II, had no effect on the uptake of the amino acid. Castanospermine (100 micrograms/ml) and 1-deoxynojirimycin (1 mM), inhibitors of glucosidases, and 1-deoxymannojirimycin (1 mM), an inhibitor of mannosidase I, reduced the rate of transport by 35-45%. All inhibitory compounds decreased the Vmax for transport without affecting the Km which suggests that inhibition of oligosaccharide trimming reduces the number of competent transporters on the surface of the plasma membrane. Returning the cells to a drug-free medium for 24 h, following a 24 h exposure, resulted in complete recovery of uptake. Treatment of cells with neuraminidase from V. cholerae also decreased the Vmax for transport by about 20%. The results suggest that: (i) a partial complex carbohydrate chain on the high-affinity transporter for acidic amino acid transmitters is sufficient for activity and (ii) sialic acid residues may be necessary for normal operation of the transporter.