Membrane ganglioside enrichment lowers the threshold for vascular endothelial cell angiogenic signaling

The cancer glycocode as a family of diagnostic biomarkers, exemplified by tumor-associated gangliosides

One unexploited family of cancer biomarkers comprise glycoproteins, carbohydrates, and glycolipids (the Tumor Glycocode).A class of glycolipid cancer biomarkers, the tumor-marker gangliosides (TMGs) are presented here as potential diagnostics for detecting cancer, especially at early stages, as the biological function of TMGs makes them etiological. We propose that a quantitative matrix of the Cancer Biomarker Glycocode and artificial intelligence-driven algorithms will expand the menu of validated cancer biomarkers as a step to resolve some of the challenges in cancer diagnosis, and yield a combination that can identify a specific cancer, in a tissue-agnostic manner especially at early stages, to enable early intervention. Diagnosis is critical to reducing cancer mortality but many cancers lack efficient and effective diagnostic tests, especially for early stage disease. Ideal diagnostic biomarkers are etiological, samples are preferably obtained via non-invasive methods (e.g. liquid biopsy of blood or urine), and are quantitated using assays that yield high diagnostic sensitivity and specificity for efficient diagnosis, prognosis, or predicting response to therapy. Validated biomarkers with these features are rare. While the advent of proteomics and genomics has led to the identification of a multitude of proteins and nucleic acid sequences as cancer biomarkers, relatively few have been approved for clinical use. The use of multiplex arrays and artificial intelligence-driven algorithms offer the option of combining data of known biomarkers; however, for most, the sensitivity and the specificity are below acceptable criteria, and clinical validation has proven difficult. One strategic solution to this problem is to expand the biomarker families beyond those currently exploited. One unexploited family of cancer biomarkers comprise glycoproteins, carbohydrates, and glycolipids (the Tumor Glycocode). Here, we focus on a family of glycolipid cancer biomarkers, the tumor-marker gangliosides (TMGs). We discuss the diagnostic potential of TMGs for detecting cancer, especially at early stages. We include prior studies from the literature to summarize findings for ganglioside quantification, expression, detection, and biological function and its role in various cancers. We highlight the examples of TMGs exhibiting ideal properties of cancer diagnostic biomarkers, and the application of GD2 and GD3 for diagnosis of early stage cancers with high sensitivity and specificity. We propose that a quantitative matrix of the Cancer Biomarker Glycocode and artificial intelligence-driven algorithms will expand the menu of validated cancer biomarkers as a step to resolve some of the challenges in cancer diagnosis, and yield a combination that can identify a specific cancer, in a tissue-agnostic manner especially at early stages, to enable early intervention.

Correlation of Serum N-Acetylneuraminic Acid with the Risk of Moyamoya Disease

N-acetylneuraminic acid (Neu5Ac) is a functional metabolite and has been demonstrated to be a risk factor for cardiovascular diseases. It is not clear whether Neu5Ac is associated with a higher risk of cerebrovascular disorders, especially moyamoya disease (MMD). We sought to elucidate the association between serum Neu5Ac levels and MMD in a case-control study and to create a clinical risk model. In our study, we included 360 MMD patients and 89 matched healthy controls (HCs). We collected the participants' clinical characteristics, laboratory results, and serum Neu5Ac levels. Increased level of serum Neu5Ac was observed in the MMD patients (p = 0.001). After adjusting for traditional confounders, the risk of MMD (odds ratio [OR]: 1.395; 95% confidence interval [CI]: 1.141-1.706) increased with each increment in Neu5Ac level (per μmol/L). The area under the curve (AUC) values of the receiver operating characteristic (ROC) curves of the basic model plus Neu5Ac binary outcomes, Neu5Ac quartiles, and continuous Neu5Ac are 0.869, 0.863, and 0.873, respectively. Furthermore, including Neu5Ac in the model offers a substantial improvement in the risk reclassification and discrimination of MMD and its subtypes. A higher level of Neu5Ac was found to be associated with an increased risk of MMD and its clinical subtypes.

The biological role and immunotherapy of gangliosides and GD3 synthase in cancers

Gangliosides are a large subfamily of glycosphingolipids that broadly exist in the nervous system and interact with signaling molecules in the lipid rafts. GD3 and GD2 are two types of disialogangliosides (GDs) that include two sialic acid residues. The expression of GD3 and GD2 in various cancers is mostly upregulated and is involved in tumor proliferation, invasion, metastasis, and immune responses. GD3 synthase (GD3S, ST8SiaI), a subclass of sialyltransferases, regulates the biosynthesis of GD3 and GD2. GD3S is also upregulated in most tumors and plays an important role in the development and progression of tumors. Many clinical trials targeting GD2 are ongoing and various immunotherapy studies targeting gangliosides and GD3S are gradually attracting much interest and attention. This review summarizes the function, molecular mechanisms, and ongoing clinical applications of GD3, GD2, and GD3S in abundant types of tumors, which aims to provide novel targets for future cancer therapy.

Salvianolic acid B, a new type I IRE1 kinase inhibitor, abrogates AngII-induced angiogenesis by interacting with IRE1 in its active conformation

Angiotensin II (AngII)-mediated pathological angiogenesis is one of the important factors promoting the progression of atherosclerosis, tumour metastasis, and diabetic retinopathy. Here, we first demonstrate that salvianolic acid B (Sal B) attenuated AngII-induced angiogenesis by downregulating the IRE1/ASK1/JNK/p38MAPK signalling pathway and protected vascular endothelial cells from hypoxia-induced damage. These pharmacological consequences could be ascribed to the unique interactions between Sal B and the ATP-binding cavity of IREIα, leading to bi-directional roles of IRE1 kinase and endonuclease activity; this may possibly be one of the essential mechanisms of the bi-directional regulation of angiogenesis in different conditions. Moreover, our results indicated that IRE1 was a novel anti-angiogenesis target and type I IRE1 kinase inhibitor (e.g., Sal B, APY29) and might be a potentially eligible low-toxicity drug for treating AngII-mediated pathological angiogenesis.

B4GALNT1 induces angiogenesis, anchorage independence growth and motility, and promotes tumorigenesis in melanoma by induction of ganglioside GM2/GD2

β-1,4-N-Acetyl-Galactosaminyltransferase 1 (B4GALNT1) encodes the key enzyme B4GALNT1 to generate gangliosides GM2/GD2. GM2/GD2 gangliosides are surface glycolipids mainly found on brain neurons as well as peripheral nerves and skin melanocytes and are reported to exacerbate the malignant potential of melanomas. In order to elucidate the mechanism, we performed functional analyses of B4GALNT1-overexpressing cells. We analyzed ganglioside pattern on four melanoma and two neuroblastoma cell lines by high performance liquid chromatography (HPLC). We overexpressed B4GALNT1 in GM2/GD2-negative human melanoma cell line (SH4) and confirmed production of GM2/GD2 by HPLC. They showed higher anchorage independence growth (AIG) in colony formation assay, and exhibited augmented motility. In vitro, cell proliferation was not affected by GM2/GD2 expression. In vivo, GM2/GD2-positive SH4 clones showed significantly higher tumorigenesis in NOD/Scid/IL2Rγ-null mice, and immunostaining of mouse CD31 revealed that GM2/GD2 induced remarkable angiogenesis. No differences were seen in melanoma stem cell and Epithelial-Mesenchymal Transition markers between GM2/GD2-positive and -negative SH4 cells. We therefore concluded that B4GALNT1, and consequently GM2/GD2, enhanced tumorigenesis via induction of angiogenesis, AIG, and cell motility. RNA-Seq suggested periostin as a potential key factor for angiogenesis and AIG. These findings may lead to development of novel therapy for refractory melanoma.

Biological Functions and Analytical Strategies of Sialic Acids in Tumor

Sialic acids, a subset of nine carbon acidic sugars, often exist as the terminal sugars of glycans on either glycoproteins or glycolipids on the cell surface. Sialic acids play important roles in many physiological and pathological processes via carbohydrate-protein interactions, including cell-cell communication, bacterial and viral infections. In particular, hypersialylation in tumors, as well as their roles in tumor growth and metastasis, have been widely described. Recent studies have indicated that the aberrant sialylation is a vital way for tumor cells to escape immune surveillance and keep malignance. In this article, we outline the present state of knowledge on the metabolic pathway of human sialic acids, the function of hypersialylation in tumors, as well as the recent labeling and analytical techniques for sialic acids. It is expected to offer a brief introduction of sialic acid metabolism and provide advanced analytical strategies in sialic acid studies.

Vascular Diseases and Gangliosides

Vascular diseases, such as myocardial infarction and cerebral infarction, are most commonly caused by atherosclerosis, one of the leading causes of death worldwide. Risk factors for atherosclerosis include lifestyle and aging. It has been reported that lifespan could be extended in mice by targeting senescent cells, which led to the suppression of aging-related diseases, such as vascular diseases. However, the molecular mechanisms underlying the contribution of aging to vascular diseases are still not well understood. Several types of cells, such as vascular (endothelial cell), vascular-associated (smooth muscle cell and fibroblast) and inflammatory cells, are involved in plaque formation, plaque rupture and thrombus formation, which result in atherosclerosis. Gangliosides, a group of glycosphingolipids, are expressed on the surface of vascular, vascular-associated and inflammatory cells, where they play functional roles. Clarifying the role of gangliosides in atherosclerosis and their relationship with aging is fundamental to develop novel prevention and treatment methods for vascular diseases based on targeting gangliosides. In this review, we highlight the involvement and possible contribution of gangliosides to vascular diseases and further discuss their relationship with aging.

Neuronal Signaling by Thy-1 in Nanodomains With Specific Ganglioside Composition: Shall We Open the Door to a New Complexity?

Thy-1 is a small membrane glycoprotein and member of the immunoglobulin superfamily of cell adhesion molecules. It is abundantly expressed in many cell types including neurons and is anchored to the outer membrane leaflet via a glycosyl phosphatidylinositol tail. Thy-1 displays a number of interesting properties such as fast lateral diffusion, which allows it to get in and out of membrane nanodomains with different lipid composition. Thy-1 displays a broad expression in different cell types and plays confirmed roles in cell development, adhesion and differentiation. Here, we explored the functions of Thy-1 in neuronal signaling, initiated by extracellular binding of α_Vβ₃ integrin, may strongly dependent on the lipid content of the cell membrane. Also, we assort literature suggesting the association of Thy-1 with specific components of lipid rafts such as sialic acid containing glycosphingolipids, called gangliosides. Furthermore, we argue that Thy-1 positioning in nanodomains may be influenced by gangliosides. We propose that the traditional conception of Thy-1 localization in rafts should be reconsidered and evaluated in detail based on the potential diversity of neuronal nanodomains.

Sialic acid as a target for the development of novel antiangiogenic strategies

Sialic acid is associated with glycoproteins and gangliosides of eukaryotic cells. It regulates various molecular interactions, being implicated in inflammation and cancer, where its expression is regulated by sialyltransferases and sialidases. Angiogenesis, the formation of new capillaries, takes place during inflammation and cancer, and represents the outcome of several interactions occurring at the endothelial surface among angiogenic growth factors, inhibitors, receptors, gangliosides and cell-adhesion molecules. Here, we elaborate on the evidences that many structures involved in angiogenesis are sialylated and that their interactions depend on sialic acid with implications in angiogenesis itself, inflammation and cancer. We also discuss the possibility to exploit sialic acid as a target for the development of novel antiangiogenic drugs.

The function of cancer-shed gangliosides in macrophage phenotype: involvement with angiogenesis

Tumor-derived gangliosides in the tumor microenvironment are involved in the malignant progression of cancer. However, the molecular mechanisms underlying the effects of gangliosides shed from tumors on macrophage phenotype remain unknown. Here, we showed that ganglioside GM1 highly induced the activity and expression of arginase-1 (Arg-1), a major M2 macrophage marker, compared to various gangliosides in bone marrow-derived macrophages (BMDM), peritoneal macrophages and Raw264.7 macrophage cells. We found that GM1 bound to macrophage mannose receptor (MMR/CD206) and common gamma chain (γc). In addition, GM1 increased Arg-1 expression through CD206 and γc-mediated activation of Janus kinase 3 (JAK3) and signal transducer and activator of transcription- 6 (STAT-6). Interestingly, GM1-stimulated macrophages secreted monocyte chemoattractant protein-1 (MCP-1/CCL2) through a CD206/γc/STAT6-mediated signaling pathway and induced angiogenesis. Moreover, the angiogenic effect of GM1-treated macrophages was diminished by RS102895, an MCP-1 receptor (CCR2) antagonist. From these results we suggest that tumor-shed ganglioside is a secretory factor regulating the phenotype of macrophages and consequently enhancing angiogenesis.

Glycosylation as a Main Regulator of Growth and Death Factor Receptors Signaling

Glycosylation is a very frequent and functionally important post-translational protein modification that undergoes profound changes in cancer. Growth and death factor receptors and plasma membrane glycoproteins, which upon activation by extracellular ligands trigger a signal transduction cascade, are targets of several molecular anti-cancer drugs. In this review, we provide a thorough picture of the mechanisms bywhich glycosylation affects the activity of growth and death factor receptors in normal and pathological conditions. Glycosylation affects receptor activity through three non-mutually exclusive basic mechanisms: (1) by directly regulating intracellular transport, ligand binding, oligomerization and signaling of receptors; (2) through the binding of receptor carbohydrate structures to galectins, forming a lattice thatregulates receptor turnover on the plasma membrane; and (3) by receptor interaction with gangliosides inside membrane microdomains. Some carbohydrate chains, for example core fucose and β1,6-branching, exert a stimulatory effect on all receptors, while other structures exert opposite effects on different receptors or in different cellular contexts. In light of the crucial role played by glycosylation in the regulation of receptor activity, the development of next-generation drugs targeting glyco-epitopes of growth factor receptors should be considered a therapeutically interesting goal.

Gangliosides drive the tumor infiltration and function of myeloid-derived suppressor cells

Although it is now widely appreciated that antitumor immunity is critical to impede tumor growth and progression, there remain significant gaps in knowledge about the mechanisms used by tumors to escape immune control. In tumor cells, we hypothesized that one mechanism of immune escape used by tumors involves the synthesis and extracellular shedding of gangliosides, a class of biologically active cell surface glycosphingolipids with known immunosuppressive properties. In this study, we report that tumor cells engineered to be ganglioside deficient exhibit impaired tumorigenicity, supporting a link between ganglioside-dependent immune escape and tumor outgrowth. Notably, we documented a dramatic reduction in the numbers and function of tumor-infiltrating myeloid-derived suppressor cells (MDSC) in ganglioside-deficient tumors, in contrast with the large MDSC infiltrates seen in ganglioside-rich littermate control tumors. Transient ganglioside reconstitution of the tumor cell inoculum was sufficient to increase MDSC infiltration, supporting a direct connection between ganglioside production by tumor cells and the recruitment of immunosuppressive MDSC into the tumor microenvironment. Our results reveal a novel mechanism of immune escape that supports tumor growth, with broad implications given that many human tumors produce and shed high levels of gangliosides.

Molecular recognition of gangliosides and their potential for cancer immunotherapies

Gangliosides are sialic-acid-containing glycosphingolipids expressed on all vertebrate cells. They are primarily positioned in the plasma membrane with the ceramide part anchored in the membrane and the glycan part exposed on the surface of the cell. These lipids have highly diverse structures, not the least with respect to their carbohydrate chains, with N-acetylneuraminic acid (NeuAc) and N-glycolylneuraminic acid (NeuGc) being the two most common sialic-acid residues in mammalian cells. Generally, human healthy tissue is deficient in NeuGc, but this molecule is expressed in tumors and in human fetal tissues, and was hence classified as an onco-fetal antigen. Gangliosides perform important functions through carbohydrate-specific interactions with proteins, for example, as receptors in cell–cell recognition, which can be exploited by viruses and other pathogens, and also by regulating signaling proteins, such as the epidermal growth factor receptor (EGFR) and the vascular endothelial growth factor receptor (VEGFR), through lateral interaction in the membrane. Through both mechanisms, tumor-associated gangliosides may affect malignant progression, which makes them attractive targets for cancer immunotherapies. In this review, we describe how proteins recognize gangliosides, focusing on the molecular recognition of gangliosides associated with cancer immunotherapy, and discuss the importance of these molecules in cancer research.

A monophasic extraction strategy for the simultaneous lipidome analysis of polar and nonpolar retina lipids

Lipid extraction using a monophasic chloroform/methanol/water mixture, coupled with functional group selective derivatization and direct infusion nano-ESI-high-resolution/accurate MS, is shown to facilitate the simultaneous analysis of both highly polar and nonpolar lipids from a single retina lipid extract, including low abundance highly polar ganglioside lipids, nonpolar sphingolipids, and abundant glycerophospholipids. Quantitative comparison showed that the monophasic lipid extraction method yielded similar lipid distributions to those obtained from established "gold standard" biphasic lipid extraction methods known to enrich for either highly polar gangliosides or nonpolar lipids, respectively, with only modest relative ion suppression effects. This improved lipid extraction and analysis strategy therefore enables detailed lipidome analyses of lipid species across a broad range of polarities and abundances, from minimal amounts of biological samples and without need for multiple lipid class-specific extractions or chromatographic separation prior to analysis.

Glycobiology of neuroblastoma: impact on tumor behavior, prognosis, and therapeutic strategies

Neuroblastoma (NB), accounting for 10% of childhood cancers, exhibits aberrant cell-surface glycosylation patterns. There is evidence that changes in glycolipids and protein glycosylation pathways are associated to NB biological behavior. Polysialic acid (PSA) interferes with cellular adhesion, and correlates with NB progression and poor prognosis, as well as the expression of sialyltransferase STX, the key enzyme responsible for PSA synthesis. Galectin-1 and gangliosides, overexpressed and actively shedded by tumor cells, can modulate normal cells present in the tumor microenvironment, favoring angiogenesis and immunological escape. Different glycosyltransferases are emerging as tumor markers and potential molecular targets. Immunotherapy targeting disialoganglioside GD2 rises as an important treatment option. One anti-GD2 antibody (ch14.18), combined with IL-2 and GM-CSF, significantly improves survival for high-risk NB patients. This review summarizes our current knowledge on NB glycobiology, highlighting the molecular basis by which carbohydrates and protein–carbohydrate interactions impact on biological behavior and patient clinical outcome.

How Do Gangliosides Regulate RTKs Signaling?

Gangliosides, the glycosphingolipids carrying one or several sialic acid residues, are located on the outer leaflet of the plasma membrane in glycolipid-enriched microdomains, where they interact with molecules of signal transduction pathways including receptors tyrosine kinases (RTKs). The role of gangliosides in the regulation of signal transduction has been reported in many cases and in a large number of cell types. In this review, we summarize the current knowledge on the biosynthesis of gangliosides and the mechanism by which they regulate RTKs signaling.

Tumor gangliosides accelerate murine tumor angiogenesis

Tumor cells shed gangliosides and populate their microenvironment with these biologically active membrane glycosphingolipids. In vitro, ganglioside enrichment amplifies receptor tyrosine kinase signaling and activation of vascular endothelial cells. However, a long-standing question is whether in the actual microenvironment of a neoplasm, in vivo, tumor cell ganglioside shedding stimulates angiogenesis. Here we tested the hypothesis that tumor gangliosides have a critical proangiogenic role in vivo using novel murine tumor cells, GM3synthase/GM2synthase double knockout (DKO) cells, genetically completely incapable of ganglioside synthesis and impaired in tumor growth versus wild-type (WT) ganglioside-rich cells. We studied angiogenesis during tumor formation by these ganglioside-depleted cells, quantifying vessel formation, angiogenic factor production/release, and consequences of reconstitution with purified WT gangliosides. DKO cells formed virtually avascular tumors, much smaller than ganglioside-rich WT tumors and displaying a striking paucity of blood vessels, despite levels of VEGF and other angiogenic factors that were similar to those of WT cells. Transient enrichment of the ganglioside milieu of the DKO cell inoculum by adding purified WT gangliosides partially restored angiogenesis and tumor growth. We conclude that tumor gangliosides trigger robust angiogenesis important for tumor growth. Our findings suggest strategies to eliminate their synthesis and shedding by tumor cells should be pursued.

A hybrid model of the role of VEGF binding in endothelial cell migration and capillary formation

Vascular endothelial growth factor (VEGF) is the most studied family of soluble, secreted mediators of endothelial cell migration, survival, and proliferation. VEGF exerts its function by binding to specific tyrosine kinase receptors on the cell surface and transducing the effect through downstream signaling. In order to study the influence of VEGF binding on endothelial cell motion, we develop a hybrid model of VEGF-induced angiogenesis, based on the theory of reinforced random walks. The model includes the chemotactic response of endothelial cells to angiogenic factors bound to cell-surface receptors, rather than approximating this as a function of extracellular chemical concentrations. This allows us to capture biologically observed phenomena such as activation and polarization of endothelial cells in response to VEGF gradients across their lengths, as opposed to extracellular gradients throughout the tissue. We also propose a novel and more biologically reasonable functional form for the chemotactic sensitivity of endothelial cells, which is also governed by activated cell-surface receptors. This model is able to predict the threshold level of VEGF required to activate a cell to move in a directed fashion as well as an optimal VEGF concentration for motion. Model validation is achieved by comparison of simulation results directly with experimental data.

Ganglioside GM3 participates in the TGF-β1-induced epithelial-mesenchymal transition of human lens epithelial cells

TGF-β (transforming growth factor-β)-induced EMT (epithelial-mesenchymal transition) induces the proliferation and migration of the HLE (human lens epithelial) cells. Ganglioside GM3, simple sialic-acid-containing glycosphingolipids on mammalian cell membranes, regulates various pathological phenomena such as insulin resistance and tumour progression. However, the relationship between ganglioside GM3 and TGF-β-induced EMT in the HLE B-3 cells is poorly understood. In the present study we demonstrated that ganglioside GM3 was involved in TGF-β1-induced EMT in HLE B-3 cells. Our results indicated that the expression of ganglioside GM3 and GM3 synthase mRNA were significantly increased in TGF-β1-induced HLE B-3 cells. Reporter gene analysis also demonstrated that transcriptional activation of the GM3 synthase gene was regulated by Sp1 (specificity protein 1) in HLE B-3 cells upon TGF-β1 stimulation. Interestingly, the inhibition of ganglioside GM3 expression by d-PDMP [d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol] and GM3 synthase shRNA (short hairpin RNA) resulted significantly in the suppression of cell migration and EMT-related signalling in HLE B-3 cells stimulated by TGF-β. Furthermore, exogenous treatment of ganglioside GM3 rescued the expression of EMT molecules and cell migration suppressed by the depletion of ganglioside GM3 in TGF-β1-induced HLE B-3 cells. We also found that ganglioside GM3 interacted with TGFβRs (TGF-β receptors) in TGF-β1-induced HLE B-3 cells. Taken together, these results suggest that ganglioside GM3 induced by TGF-β1 regulates EMT by potential interaction with TGFβRs.

Gene expression analysis in human breast cancer associated blood vessels

Angiogenesis is essential for solid tumour growth, whilst the molecular profiles of tumour blood vessels have been reported to be different between cancer types. Although presently available anti-angiogenic strategies are providing some promise for the treatment of some cancers it is perhaps not surprisingly that, none of the anti-angiogenic agents available work on all tumours. Thus, the discovery of novel anti-angiogenic targets, relevant to individual cancer types, is required. Using Affymetrix microarray analysis of laser-captured, CD31-positive blood vessels we have identified 63 genes that are upregulated significantly (5-72 fold) in angiogenic blood vessels associated with human invasive ductal carcinoma (IDC) of the breast as compared with blood vessels in normal human breast. We tested the angiogenic capacity of a subset of these genes. Genes were selected based on either their known cellular functions, their enriched expression in endothelial cells and/or their sensitivity to anti-VEGF treatment; all features implicating their involvement in angiogenesis. For example, RRM2, a ribonucleotide reductase involved in DNA synthesis, was upregulated 32-fold in IDC-associated blood vessels; ATF1, a nuclear activating transcription factor involved in cellular growth and survival was upregulated 23-fold in IDC-associated blood vessels and HEX-B, a hexosaminidase involved in the breakdown of GM2 gangliosides, was upregulated 8-fold in IDC-associated blood vessels. Furthermore, in silico analysis confirmed that AFT1 and HEX-B also were enriched in endothelial cells when compared with non-endothelial cells. None of these genes have been reported previously to be involved in neovascularisation. However, our data establish that siRNA depletion of Rrm2, Atf1 or Hex-B had significant anti-angiogenic effects in VEGF-stimulated ex vivo mouse aortic ring assays. Overall, our results provide proof-of-principle that our approach can identify a cohort of potentially novel anti-angiogenic targets that are likley to be, but not exclusivley, relevant to breast cancer.

NEU1 and NEU3 sialidase activity expressed in human lung microvascular endothelia: NEU1 restrains endothelial cell migration, whereas NEU3 does not

The microvascular endothelial surface expresses multiple molecules whose sialylation state regulates multiple aspects of endothelial function. To better regulate these sialoproteins, we asked whether endothelial cells (ECs) might express one or more catalytically active sialidases. Human lung microvascular EC lysates contained heat-labile sialidase activity for a fluorogenic substrate, 2'-(4-methylumbelliferyl)-α-D-N-acetylneuraminic acid (4-MU-NANA), that was dose-dependently inhibited by the competitive sialidase inhibitor, 2,3-dehydro-2-deoxy-N-acetylneuraminic acid but not its negative control. The EC lysates also contained sialidase activity for a ganglioside mixture. Using real time RT-PCR to detect mRNAs for the four known mammalian sialidases, NEU1, -2, -3, and -4, NEU1 mRNA was expressed at levels 2700-fold higher that those found for NEU2, -3, or -4. Western analyses indicated NEU1 and -3 protein expression. Using confocal microscopy and flow cytometry, NEU1 was immunolocalized to both the plasma membrane and the perinuclear region. NEU3 was detected both in the cytosol and nucleus. Prior siRNA-mediated knockdown of NEU1 and NEU3 each decreased EC sialidase activity for 4-MU-NANA by >65 and >17%, respectively, and for the ganglioside mixture by 0 and 40%, respectively. NEU1 overexpression in ECs reduced their migration into a wound by >40%, whereas NEU3 overexpression did not. Immunohistochemical studies of normal human tissues immunolocalized NEU1 and NEU3 proteins to both pulmonary and extrapulmonary vascular endothelia. These combined data indicate that human lung microvascular ECs as well as other endothelia express catalytically active NEU1 and NEU3. NEU1 restrains EC migration, whereas NEU3 does not.

Androgen-regulated transcriptional control of sialyltransferases in prostate cancer cells

The expression of gangliosides is often associated with cancer progression. Sialyltransferases have received much attention in terms of their relationship with cancer because they modulate the expression of gangliosides. We previously demonstrated that GD1a production was high in castration-resistant prostate cancer cell lines, PC3 and DU145, mainly due to their high expression of β-galactoside α2,3-sialyltransferase (ST3Gal) II (not ST3Gal I), and the expression of both ST3Gals was regulated by NF-κB, mainly by RelB. We herein demonstrate that GD1a was produced in abundance in cancerous tissue samples from human patients with hormone-sensitive prostate cancers as well as castration-resistant prostate cancers. The expression of ST3Gal II was constitutively activated in castration-resistant prostate cancer cell lines, PC3 and DU145, because of the hypomethylation of CpG island in its promoter. However, in androgen-depleted LNCap cells, a hormone-sensitive prostate cancer cell line, the expression of ST3Gal II was silenced because of the hypermethylation of the promoter region. The expression of ST3Gal II in LNCap cells increased with testosterone treatment because of the demethylation of the CpG sites. This testosterone-dependent ST3Gal II expression was suppressed by RelB siRNA, indicating that RelB activated ST3Gal II transcription in the testosterone-induced demethylated promoter. Therefore, in hormone-sensitive prostate cancers, the production of GD1a may be regulated by androgen. This is the first report indicating that the expression of a sialyltransferase is transcriptionally regulated by androgen-dependent demethylation of the CpG sites in its gene promoter.

GD1a modulates GM-CSF-induced cell proliferation

Gangliosides have been extensively described to be involved in the proliferation and differentiation of various cell types, such including hematopoietic cells. Our previous studies on murine models of stroma-mediated myelopoiesis have shown that gangliosides are required for optimal capacity of stromal cells to support proliferation of myeloid precursor cells, being shed to the supernatant and selectively incorporated into myeloid cell membranes. Here we describe the effect of gangliosides on the specific granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced proliferation. For that, we used the monocytic FDC-P1 cell line, which is dependent upon GM-CSF for survival and proliferation. Cells were cultured in the presence of GM-CSF and exogenous gangliosides (GM3, GD1a or GM1) or in the absence of endogenous ganglioside synthesis by the use of a ceramide-synthase inhibitor, D-PDMP. We observed that exogenous addition of GD1a enhanced the GM-CSF-induced proliferation of the FDC-P1 cells. Also, we detected an increase in the expression of the α isoform of the GM-CSF receptor (GMRα) as well as of the transcription factor C/EBPα. On the contrary, inhibition of glucosylceramide synthesis was accompanied by a decrease in cell proliferation, which was restored upon the addition of exogenous GD1a. We also show a co-localization of GD1a and GMR by immunocytochemistry. Taken together, our results suggest for the first time that ganglioside GD1a play a role on the modulation of GM-CSF-mediated proliferative response, which might be of great interest not only in hematopoiesis, but also in other immunological processes, Alzheimer disease, alveolar proteinosis and wherever GM-CSF exerts its effects.

Immunohistochemical Reactivity of the 14F7 Monoclonal Antibody Raised against N-Glycolyl GM3 Ganglioside in Some Benign and Malignant Skin Neoplasms

The evaluation of 14F7 Mab (anti-N-glycolyl GM3 ganglioside) immunorecognition in normal skin, cutaneous malignant melanoma (CMM), and in lymph node metastases (LNM) has been previously reported. In this work we extended the study to benign (BMN) and dysplastic (DMN) melanocytic nevi, basal (BCC), and squamous cell carcinoma (SCC). Immunohistochemical assays with 14F7 followed by a biotinylated link universal and streptavidin-AP in normal and pathological tissues were made. No reaction of 14F7 in normal skin (0/10) as well as a low reactivity in BMN (2/11) and DMN (1/7) was detected. A limited staining in BCC (2/13) and in SCC (4/8) was also evidenced, while 14F7 Mab were mostly reactive in CMM (28/28) and in LNM (6/7). These results suggest that 14F7 reactivity could be closely related with the more aggressive biological behavior of CMM and also support the use of NeuGcGM3 as target for both passive and active melanoma immunotherapy.

Ganglioside-exposed dendritic cells inhibit T-cell effector function by promoting regulatory cell activity

Tumour pathogenesis is characterized by an immunosuppressive microenvironment that limits the development of effective tumour-specific immune responses. This is in part the result of tumour-dependent recruitment and activation of regulatory cells, such as myeloid-derived suppressor cells and regulatory T cells in the tumour microenvironment and draining lymph nodes. Shedding of gangliosides by tumour cells has immunomodulatory properties, suggesting that gangliosides may be a critical factor in initiating an immunosuppressive microenvironment. To better define the immunomodulatory properties of gangliosides on antigen-specific T-cell activation and development we have developed an in vitro system using ganglioside-treated murine bone-marrow-derived dendritic cells to prime and activate antigen-specific CD4(+) T cells from AND T-cell receptor transgenic mice. Using this system, ganglioside treatment promotes the development of a dendritic cell population characterized by decreased CD86 (B7-2) expression, and decreased interleukin-12 and interleukin-6 production. When these cells are used as antigen-presenting cells, CD4 T cells are primed to proliferate normally, but have a defect in T helper (Th) effector cell development. This defect in Th effector cell responses is associated with the development of regulatory T-cell activity that can suppress the activation of previously primed Th effector cells in a contact-dependent manner. In total, these data suggest that ganglioside-exposed dendritic cells promote regulatory T-cell activity that may have long-lasting effects on the development of tumour-specific immune responses.

Ganglioside synthase knockout in oncogene-transformed fibroblasts depletes gangliosides and impairs tumor growth

Biologically active membrane gangliosides, expressed and released by many human tumors, are hypothesized to significantly impact tumor progression. Lack of a model of complete and specific tumor ganglioside depletion in vivo, however, has hampered elucidation of their role. Here we report the creation of a novel, stable, genetically induced tumor cell system resulting in specific and complete blockade of ganglioside synthesis. Wild type (WT) and GM3 synthase/GM2 synthase double knockout (DKO) murine embryonic fibroblasts were transformed using amphotropic retrovirus-transduced oncogenes (pBABE-c-Myc^T58A+H-Ras^G12V). The transformed cells, WT_t and DKO_t respectively, evidenced comparable integrated copy numbers and oncogene expression. Ganglioside synthesis was completely blocked in the DKO_t cells, importantly without triggering an alternate pathway of ganglioside synthesis. Ganglioside depletion (to <0.5 nmol/10⁷ cells from 9-11 nmol/10⁷ WT_t or untransfected normal fibroblasts) did not adversely affect cell proliferation kinetics but did reduce cell migration on fibronectin-coated wells, consistent with our previous observations in ganglioside-depleted normal human fibroblasts. Strikingly, despite similar oncogene expression and growth kinetics, DKO_t cells evidenced significantly impaired tumor growth in syngeneic immunocompetent mice, underscoring the pivotal role of tumor cell gangliosides and providing an ideal system for probing their mechanisms of action in vivo.

Controlled growth factor delivery for tissue engineering

Growth factors play a crucial role in information transfer between cells and their microenvironment in tissue engineering and regeneration. They initiate their action by binding to specific receptors on the surface of target cells and the chemical identity, concentration, duration, and context of these growth factors contain information that dictates cell fate. Hence, the importance of exogenous delivery of these molecules in tissue engineering is unsurprising, considering their importance for tissue regeneration. However, the short half-lives of growth factors, their relatively large size, slow tissue penetration, and their potential toxicity at high systemic levels, suggest that conventional routes of administration are unlikely to be effective. In this review, we provide an overview of the design criteria for growth factor delivery vehicles with respect to the growth factor itself and the microenvironment for delivery. We discuss various methodologies that could be adopted to achieve this localized delivery, and strategies using polymers as delivery vehicles in particular.

Sialic acid feeding aged rats rejuvenates stimulated salivation and colon enteric neuron chemotypes

Old age is linked to numerous changes of body functions such as salivation, gastrointestinal motility, and permeability all linked to central and enteric nervous system decline. Thus, gut motility and barrier functions suffer. Sialic acid plays a key role in the nervous system at large and for many receptor functions specifically. Decreased sialylation in the elderly suggests an endogenous sialic acid deficit. We used a rat model of aging, to ask whether sialic acid feeding would affect (i) stimulated salivation, (ii) gut functions, and (iii) sialic acid levels and neuronal markers in brain and gut. We observed reduced levels of pilocarpine-stimulated salivation in old versus young rats and restored this function by sialic acid feeding. Brain ganglioside bound sialic acid levels were found lower in aged versus young rats, and sialic acid feeding partly restored the levels. The hypothalamic expression of cholinergic and panneuronal markers was reduced in aged rats. The expression of the nitrergic marker nNOS was increased upon sialic acid feeding in aged rats. Neither fecal output nor gut permeability was different between young and aged rats studied here, and sialic acid feeding did not alter these parameters. However, the colonic expression of specific nervous system markers nNOS and Uchl1 and the key enzyme for sialic acid synthesis GNE were differentially affected in young and aged rats by sialic acid feeding indicating that regulatory mechanisms change with age. Investigation of sialic acid supplementation as a functional nutrient in the elderly may help those who suffer from disorders of reduced salivation. Further research is needed to understand the differential effects of sialic acid feeding in young and aged rats.

Gangliosides in cell recognition and membrane protein regulation

Gangliosides, sialic acid-bearing glycosphingolipids, are expressed on all vertebrate cells, and are the major glycans on nerve cells. They are anchored to the plasma membrane through their ceramide lipids with their varied glycans extending into the extracellular space. Through sugar-specific interactions with glycan-binding proteins on apposing cells, gangliosides function as receptors in cell-cell recognition, regulating natural killer cell cytotoxicity via Siglec-7, myelin-axon interactions via Siglec-4 (myelin-associated glycoprotein), and inflammation via E-selectin. Gangliosides also interact laterally in their own membranes, regulating the responsiveness of signaling proteins including the insulin, epidermal growth factor, and vascular endothelial growth factor receptors. In these ways, gangliosides act as regulatory elements in the immune system, in the nervous system, in metabolic regulation, and in cancer progression.

Tissue micro array analysis of ganglioside N-glycolyl GM3 expression and signal transducer and activator of transcription (STAT)-3 activation in relation to dendritic cell infiltration and microvessel density in non-small cell lung cancer

BACKGROUND

Tumor immune escape and angiogenesis contribute to tumor progression, and gangliosides and activation of signal transducer and activator of transcription (STAT)-3 are implicated in these processes. As both are considered as novel therapeutic targets, we assessed the possible association of ganglioside GM3 expression and STAT3 activation with suppression of dendritic cell (DC) activation and angiogenesis in non-small cell lung cancer (NSCLC).

METHODS

Immunohistochemistry was performed on a tissue array to determine N-glycolyl GM3 (GM3) and phosphorylated STAT3 (pSTAT3) expression in 176 primary NSCLC resections. Median values of GM3 and pSTAT3 expression were used as cut off. Microvessel density (MVD) was determined by CD34 staining and morphology. CD1a and CD83 were used to determine infiltrating immature and mature dendritic cells, respectively.

RESULTS

94% and 71% of the NSCLC samples expressed GM3 and nuclear pSTAT3, respectively. Median overall survival was 40.0 months. Both low GM3 expression and high pSTAT3 expression were associated with a worse survival, which reached near significance for GM3 (P = 0.08). Microvessel density (MVD), determined by CD34 staining and morphology, was lower in NSCLC samples with high GM3 expression. CD1a+ cells (immature DCs) were more frequent in NSCLC tissues as compared to peritumoral lung tissue, while CD83+ cells (mature DCs) were more frequent in peritumoral lung tissue. CD83+ DCs were less frequent in NSCLC tissues with high GM3 expression.

CONCLUSION

GM3 and pSTAT3 are widely expressed in NSCLC. Based on CD83 expression, GM3, but not pSTAT3, appeared to be involved in tumor-induced DC suppression. pSTAT3 expression was not associated with MVD, while GM3 might play an anti-angiogenic role.

Thematic review series: sphingolipids. Ganglioside GM3 suppresses the proangiogenic effects of vascular endothelial growth factor and ganglioside GD1a

Gangliosides are sialic acid-containing glycosphingolipids that have long been associated with tumor malignancy and metastasis. Mounting evidence suggests that gangliosides also modulate tumor angiogenesis. Tumor cells shed gangliosides into the microenvironment, which produces both autocrine and paracrine effects on tumor cells and tumor-associated host cells. In this study, we show that the simple monosialoganglioside GM3 counteracts the proangiogenic effects of vascular endothelial growth factor (VEGF) and of the complex disialoganglioside GD1a. GM3 suppressed the action of VEGF and GD1a on the proliferation of human umbilical vein endothelial cells (HUVECs) and inhibited the migration of HUVECs toward VEGF as a chemoattractant. Enrichment of added GM3 in the HUVEC membrane also reduced the phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR-2) and downstream Akt. Moreover, GM3 reduced the proangiogenic effects of GD1a and growth factors in the in vivo Matrigel plug assay. Inhibition of GM3 biosynthesis with the glucosyl transferase inhibitor, N-butyldeoxynojirimycin (NB-DNJ), increased HUVEC proliferation and the phosphorylation of VEGFR-2 and Akt. The effects of NB-DNJ on HUVECs were reversed with the addition of GM3. We conclude that GM3 has antiangiogenic action and may possess therapeutic potential for reducing tumor angiogenesis.