Glycosphingolipids Research Articles

Globo-series glycosphingolipids enhance Toll-like receptor 4-mediated inflammation and play a pathophysiological role in diabetic nephropathy.

Alteration of glycosphingolipid (GSL) expression plays key roles in the pathogenesis and pathophysiology of many important human diseases, including cancer, diabetes and glycosphingolipidosis. Inflammatory processes are involved in development and progression of diabetic nephropathy, a major complication of type 2 diabetes mellitus. GSLs are known to play roles in inflammatory responses in various diseases, and levels of renal GSLs are elevated in mouse models of diabetic nephropathy; however, little is known regarding the pathophysiological role of these GSLs in this disease process. We studied proinflammatory activity of GSLs in diabetic nephropathy using spontaneously diabetic mouse strain KK. Mice were fed a high-fat diet (HFD) (60% kcal from fat) or normal diet (ND) (4.6% kcal from fat) for a period of 8 wk. HFD-feeding resulted in quantitative and qualitative changes of renal globo-series GSLs (particularly Gb3Cer), upregulation of TNF-α, and induction of renal inflammation. Gb3Cer/Gb4Cer treatment enhanced inflammatory responses via TLR4 in TLR4/MD-2 complex expressing cells, including HEK293T, mouse bone marrow-derived macrophages (BMDMs) and human monocytes. Our findings suggest that HFD-induced increase of Gb3Cer/Gb4Cer positively modulate TLR4-mediated inflammatory response, and that such GSLs play an important pathophysiological role in diabetic nephropathy.

Glycolipid iGb3 feedback amplifies innate immune responses via CD1d reverse signaling.

The cross-talk between cellular lipid metabolism and the innate immune responses remains obscure. In addition to presenting lipid antigens to Natural Killer T-cells (NKT cells), the Cluster of Differentiation 1D Glycoprotein (CD1d) might mediate reverse signaling in antigen-presenting cells (APCs). Here we found CD1d deficiency attenuated Toll-like receptor (TLR)-triggered inflammatory innate responses in macrophages and dendritic cells, protecting mice from endotoxin shock. TLR activation in macrophages induced metabolic changes of glycosphingolipids (GSLs), among which glycolipid isoglobotrihexosylceramide (iGb3) was rapidly produced. The endogenously generated iGb3 bound CD1d in endosomal compartments and then synergized with the initially activated TLR signal to induce Tyr332 phosphorylation of CD1d intracellular domain. This led to the recruitment and activation of proline-rich tyrosine kinase 2 (Pyk2). Pyk2 interacted with IκB kinase β (IKKβ) and TANK-binding kinase 1 (TBK1), and enhanced tyrosine phosphorylation of Tyr188/199 of IKKβ and Tyr179 of TBK1 and thus, their activation to promote full activation of TLR signaling. Thus, intracellular CD1d reverse signaling, triggered by endogenous iGb3, amplifies inflammatory innate responses in APCs. Our findings identify a non-canonical function of CD1d reverse signaling activated by lipid metabolite in the innate immune response.

Altering Glycosphingolipid Composition to Improve Multiple Myeloma Bone Complication

Multiple myeloma (MM) is an incurable cancer of plasma cells (PC), with a median survival of 5-7 years. Osteolytic bone disease and skeletal complications occur in more than 80% of MM patients and significantly contribute to the morbidity and mortality of these patients. Glycosphingolipid (GSL), an essential constituent of the outer leaflet of the cellular membrane, is altered in MM and other hematological cancers. We previously reported that GM3, a subtype of GSL promotes osteoclastogenesis. On the other hand, the GSL synthase inhibitor N-butyl-deoxynojirimycin (NB-DNJ) reduces myeloma bone disease in the 5TGM1 mouse model of MM. Mechanistically, NB-DNJ prevents osteoclast (OC) development and activation by disrupting RANKL-induced localization of TRAF6 and c-SRC into lipid rafts and preventing nuclear accumulation of the transcriptional activator NFATc1.Although NB-DNJ is an FDA-approved drug treating Gaucher's disease, it has many undesired off-target effects, such as inhibiting lysosomal and plasma membrane Beta-glucocerebrosidase and interfering with intestinal glucosidases which leads to gastrointestinal toxicities and severe weight loss. Therefore, more specific GSL inhibitors are required to minimize the side effects.Here we report a novel GSL inhibitor called Genz112638 with comparable effects as NB-DNJ but reduced side effects. Genz112638 inhibits both OC formation (p < 0.01) and MM cell growth (p < 0.0001) in vitro in a dose-dependent manner. Moreover, compared to NB-DNJ, Genz112638 more significantly improved bone condition and potentially reduced MM burden, as evidenced by the amelioration of bone loss in the 5TGM1 model of myeloma, and a reduction in the proportion of MM within bone marrow and spleen without obvious adverse effects (n=6) (p < 0.01).As excessive malignant PC in MM normally arise from germinal centre, we also checked the effects of Genz112638 on germinal centre reactions in wildtype mice. We found that Genz112638 suppresses the formation of germinal centre B cells in mouse spleen induced by sheep red blood cells (n=7). Thus, Genz112638 may affect the pathogenesis of MM disease at the initial stage.Taken together, our data elucidate a novel specific GSL inhibitor as a promising candidate drug relieving two main features of MM: bone destruction and tumour burden with negligible side effects. In vitro, it decreases OC differentiation and proliferation, and meanwhile decreases MM viability and proliferation. In vivo, it may suppress B cell formation in germinal centre, ameliorate bone destruction, and potentially interfere with the vicious cycle between increased OC and susceptibility to MM. In short, we provide a preclinical platform for GSL inhibition as a new tool against MM and its related complications. [Display omitted] DisclosuresHorwood:Genzyme: Research Funding.

Efficacy Evaluation of Liver-Directed Gene Therapy in Fabry Mice

Introduction: Fabry disease (FD) is an X-linked lysosomal storage disorder resulting from mutations in the gene encoding α-galactosidase A (GLA). It is characterised by the abnormal accumulation of neutral glycosphingolipids (GSL), predominantly Globotriaosylceramide (Gb3), in the lysosomes of multiple cell types including vascular endothelial cells. It is associated with early-onset stroke, cardiomyopathy, and progression to end-stage renal failure. Current standard of care for FD is enzyme replacement therapy but alternatives including allogeneic stem cell transplantation have also been explored. Fabry disease is a good model for liver-targeted gene therapy, as relatively low levels of enzyme correction may suffice to reduce storage. Additionally, a broad therapeutic window exists, and mouse models of FD enabling preclinical proof-of-concept studies are readily available. Here we report the preclinical results of adeno-associated virus (AAV) mediated, liver-targeted gene transfer of a self-complementary (sc) vector encoding a codon-optimised GLA transgene under transcriptional control of a hepatocyte-specific promoter pseudotyped with AAV8 capsid (scAAV2/8-LP1-GLAco).Methods: In this study a single dose of scAAV2/8-LP1-GLAco vectors were administered into the tail vein of homozygote GLA knockout Fabry mice at either 1 month or 3 months of age. Two doses were tested for each age group; 2x1012 vg/kg and 2x1013 vg/kg, and an additional age-matched group left as untreated to serve as an experimental control for the effects of treatment. Mice were followed in the treatment for up to 11 months before sacrificing at 11 or 14 months of age.To assess the kinetics and durability of transgene expression, plasma GLA levels were measured at various time intervals post injection.Results: Long-term follow-up of Fabry mice injected with scAAV2/8-LP1-GLAco vector demonstrated sustained, durable levels of plasma GLA throughout the typical lifespan of a mouse. Plasma GLA activity levels at 10 or 11-months post vector administration to 1 and 3-month-old mice respectively, demonstrated a dose response from 2 x 1012 to 2 x 1013 vg/kg of >1 log increase in expression. These GLA activity levels represent supra-physiological expression (x 4000 of normal levels) which resulted in uptake of GLA from the bloodstream into kidney and cardiac tissues leading to dose-dependent clearance of lipid deposits in these tissues as analysed by electron microscopy.Most importantly, sustained expression of GLA resulted in complete normalisation of Gb3 and lyso-Gb3 levels in plasma and liver tissues as quantified by mass spectrometry. Interestingly, these preclinical studies in Fabry mice at the age of 1 and 3 months demonstrated not only prevention but also reversal of lysosomal storage deposits through liver-specific expression of GLA.Finally, in these in vivo mouse studies no adverse clinical signs were observed, despite the increased plasma exposure to GLA.Conclusions: Collectively, these data provide strong evidence that our liver-directed AAV-mediated gene therapy approach holds considerable therapeutic potential for the treatment of Fabry disease. We anticipate that a single dose IV procedure will pose minimal burden to Fabry patients and will be a viable alternative to biweekly enzyme infusions, potentially reducing treatment-related morbidity whislt improving patient quality of life and potentially providing them with a functional long-term cure. DisclosuresKia:Freeline: Employment, Equity Ownership. McIntosh:Freeline: Consultancy. Hosseini:Freeline: Employment, Equity Ownership. Sheridan:Freeline: Employment, Equity Ownership. Corbau:Freeline: Employment, Equity Ownership. Nathwani:BioMarin: Consultancy, Patents & Royalties; UniQure: Patents & Royalties; Freeline: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties.

Upregulation of human glycolipid transfer protein (GLTP) induces necroptosis in colon carcinoma cells

Human GLTP on chromosome 12 (locus 12q24.11) encodes a 24 kD amphitropic lipid transfer protein (GLTP) that mediates glycosphingolipid (GSL) intermembrane trafficking and regulates GSL homeostatic levels within cells. Herein, we provide evidence that GLTP overexpression inhibits the growth of human colon carcinoma cells (HT-29; HCT-116), but spares normal colonic cells (CCD-18Co). Mechanistic studies reveal that GLTP overexpression arrested the cell cycle at the G1/S checkpoint via upregulation of cyclin-dependent kinase inhibitor-1B (Kip1/p27) and cyclin-dependent kinase inhibitor 1A (Cip1/p21) at the protein and mRNA levels, and downregulation of cyclin-dependent kinase-2 (CDK2), cyclin-dependent kinase-4 (CDK4), cyclin E and cyclin D1 protein levels. Assessment of the biological fate of HCT-116 cells overexpressing GLTP indicated no increase in cell death suggesting induction of quiescence. However, HT-29 cells overexpressing GLTP underwent cell death by necroptosis as revealed by phosphorylation of human mixed lineage kinase domain-like protein (pMLKL) via receptor-interacting protein kinase-3 (RIPK-3), elevated cytosolic calcium, and plasma membrane permeabilization by pMLKL oligomerization. Overexpression of W96A-GLTP, an ablated GSL binding site mutant, failed to arrest the cell cycle or induce necroptosis. Sphingolipid assessment (ceramide, monohexosylceramide, sphingomyelin, ceramide-1-phosphate, sphingosine, and sphingosine-1-phosphate) of HT-29 cells overexpressing GLTP revealed large decreases (>5-fold) in sphingosine-1-phosphate with minimal change in 16:0-ceramide, tipping the ‘sphingolipid rheostat’ (S1P/16:0-Cer ratio) towards cell death. Depletion of RIPK-3 or MLKL abrogated necroptosis induced by GLTP overexpression. Our findings establish GLTP upregulation as a previously unknown suppressor of human colon carcinoma HT-29 cells via interference with cell cycle progression and induction of necroptosis.

Dissociation of globotriaosylceramide and impaired endothelial function in α-galactosidase-A deficient EA.hy926 cells

Fabry disease, a rare, X-linked lysosomal storage disease, arises from deficiency of the lysosomal hydrolase, α-galactosidase A (GLA) which disrupts the catabolism of globo- series glycosphingolipids (GSLs). One potential link between GLA deficiency and vascular dysfunction may be changes in endothelial nitric oxide synthase (eNOS) function. GLA-deficient EA.hy926 cells were obtained by siRNA knockdown of GLA expression and by mutation of GLA with CRISPR/Cas9 gene editing to investigate the effects of GLA deficiency on eNOS. As previously observed with siRNA knockdown of GLA, globotriaosylceramide (Gb3) accumulated in EA.hy926 cells. In contrast, Gb3 did not accumulate in CRISPR/Cas9 gene edited GLA-deficient cells, but instead, globotetraosylceramide (Gb4). However, in both the siRNA and CRISPR/Cas9 models globotriaosylsphingosine (lyso-Gb3) was elevated. As was previously observed with siRNA knockdown of GLA expression, CRISPR/Cas9 GLA-deficient cells had lower eNOS activity. Restoring GLA activity in GLA-deficient cells with exogenous GLA treatment improved eNOS activity. In contrast, treating cells with the glucosylceramide synthase inhibitor, eliglustat, decreased NOS activity. These results suggest that eNOS uncoupling is due to GLA deficiency, and not necessarily due to elevated Gb3 per se. It was observed that lyso-Gb3 inhibits eNOS activity.

The regulatory roles of glycosphingolipid-enriched lipid rafts in immune systems.

Lipid rafts formed by glycosphingolipids (GSLs) on cellular membranes play important roles in innate and adaptive immunity. Lactosylceramide (LacCer) forms lipid rafts on plasma and granular membranes of human neutrophils. These LacCer-enriched lipid rafts bind directly to pathogenic components, such as pathogenic fungi-derived β-glucan and Mycobacteria-derived lipoarabinomannan via carbohydrate-carbohydrate interactions, and mediate innate immune responses to these pathogens. In contrast, a-series and o-series gangliosides form distinct rafts on CD4+ and CD8+ T cell subsets, respectively, contributing to the respective functions of these cells and stimulating adaptive immune responses through T cell receptors. These findings suggest that gangliosides play indispensable roles in T cell selection and activation. This Review introduces the involvement of GSL-enriched lipid rafts in innate and adaptive immunity.

The glycosphingolipid MacCer promotes synaptic bouton formation in Drosophila by interacting with Wnt.

Lipids are structural components of cellular membranes and signaling molecules that are widely involved in development and diseases, but the underlying molecular mechanisms are poorly understood, partly because of the vast variety of lipid species and complexity of synthetic and turnover pathways. From a genetic screen, we identify that mannosyl glucosylceramide (MacCer), a species of glycosphingolipid (GSL), promotes synaptic bouton formation at the Drosophila neuromuscular junction (NMJ). Pharmacological and genetic analysis shows that the NMJ growth-promoting effect of MacCer depends on normal lipid rafts, which are known to be composed of sphingolipids, sterols and select proteins. MacCer positively regulates the synaptic level of Wnt1/Wingless (Wg) and facilitates presynaptic Wg signaling, whose activity is raft-dependent. Furthermore, a functional GSL-binding motif in Wg exhibiting a high affinity for MacCer is required for normal NMJ growth. These findings reveal a novel mechanism whereby the GSL MacCer promotes synaptic bouton formation via Wg signaling.

Sialic Acid Linkage Specific Derivatization of Glycosphingolipid Glycans by Ring-Opening Aminolysis of Lactones

Sialic acids occur widely as glycoconjugates at the nonreducing ends of glycans. Glycosphingolipids (GSLs) include a large number of sialyl-linked glycan isomers with α2,3-, α2,6-, and α2,8-linked polysialic acids. Thus, it is difficult to distinguish structural isomers with the same mass by mass spectrometry. The sialic acid linkage specific alkylamidation (SALSA) method has been developed for discriminating between α2,3- and α2,6-linked isomers, but sequential amidation of linkage-specific sialic acids is generally complicated and time-consuming. Moreover, analysis of GSL-glycans containing α2,8-linked polysialic acids using solid-phase SALSA has not been reported. Herein, we report a novel SALSA method focused on ring-opening aminolysis (aminolysis-SALSA), which shortens the reaction time and simplifies the experimental procedures. We demonstrate that aminolysis-SALSA can successfully distinguish serum GSL-glycan isomers by mass spectrometry. In addition, ring-opening aminolysis can easily be applied to amine and hydrazine derivatives.

A bioinformatics study on the mechanism of lipopolysaccharide-induced mouse lung fibroblast aerobic glycolysis

Objective To investigate the molecular mechanism of lipopolysaccharide (LPS)-induced aerobic glycolysis of lung fibroblasts in vitro to identify the pathogenesis of sepsis associated pulmonary fibrosis. Methods Primary cultured mouse lung fibroblasts were seeded in 6-well plates and were divided into 4 groups(n=3) according to random number table as follows: PBS control group(group Con), LPS 0.5 mg/L(group LPS0.5), LPS 2.0 mg/L(group LPS2.0) and LPS 4.0 mg/L(group LPS4.0). PBS and the corresponding concentrations of LPS were added to cultured fibroblasts. After incubating for 24 h, ELISA was used to detect the level of lactic acid in the supernatant of lung fibroblasts after stimulation of LPS with different concentrations. Gene-chip was used to detect differentially expressed genes of mouse lung fibroblasts between LPS group and PBS group. Also, KEGG pathway enrichment analysis was performed to explore glycometabolism related signaling pathways to clarify the mechanisms of LPS-induced aerobic glycolysis of mouse lung fibroblasts. Results The expression of lactic acid in the supernatant in group LPS0.5 (P<0.05), group LPS2.0 (P<0.05) and group LPS4.0(P<0.05) was significantly higher than group Con. The tendency of increasing is corresponded to LPS concentration raising. DNA microarray data screened out differentially expressed genes between LPS group and group Con. Four enrichment pathways is closely related to glycometabolism obtained, including insulin signaling pathway, janus kinase/signal transducers and activators of transcription(JAK-STAT) signaling pathway, fatty acid metabolism, glycosphingolipid biosynthesis-lacto and neolacto series pathway. Conclusions LPS could initiate the process of aerobic glycolysis and promote the production of lactic acid in lung fibroblasts, which is associated with insulin signaling pathway, JAK-STAT signaling pathway, fatty acid metabolism and glycosphingolipid biosynthesis-lacto and neolacto series pathway. It may be one of the internal mechanisms of the pathogenesis of sepsis-associated pulmonary fibrosis. Key words: Lipopolysaccharide; Lung fibroblast; Pulmonary fibrosis; Aerobic glycolysis

Separation of glycosphingolipids with titanium dioxide.

We introduce the principle of a new technique to isolate glycosphingolipids (GSLs) from phospholipids. Neutral and acidic GSLs in organic solvent bind to titanium dioxide under neutral pH and can be eluted with 5mg/ml of 2,5-dihydroxybenzoic acid in methanol. This special property is applicable for eliminating phospholipids, including sphingomyelin, which cannot be eliminated by a typical mild alkaline treatment. By using this technique, we demonstrated the rapid separation of minor components of GSLs, namely sulfatide and gangliosides from rabbit serum and liver, respectively. The minor GSL components were effectively purified despite both sources containing tremendous amount of phospholipids and simple lipids such as cholesterol, cholesteryl esters and triglycerides.

Structural analyses of 4-phosphate adaptor protein 2 yield mechanistic insights into sphingolipid recognition by the glycolipid transfer protein family

The glycolipid transfer protein (GLTP) fold defines a superfamily of eukaryotic proteins that selectively transport sphingolipids (SLs) between membranes. However, the mechanisms determining the protein selectivity for specific glycosphingolipids (GSLs) are unclear. Here, we report the crystal structure of the GLTP homology (GLTPH) domain of human 4-phosphate adaptor protein 2 (FAPP2) bound with N-oleoyl-galactosylceramide. Using this domain, FAPP2 transports glucosylceramide from its cis-Golgi synthesis site to the trans-Golgi for conversion into complex GSLs. The FAPP2-GLTPH structure revealed an element, termed the ID loop, that controls specificity in the GLTP family. We found that, in accordance with FAPP2 preference for simple GSLs, the ID loop protrudes from behind the SL headgroup-recognition center to mitigate binding by complex GSLs. Mutational analyses including GLTP and FAPP2 chimeras with swapped ID loops supported the proposed restrictive role of the FAPP2 ID loop in GSL selectivity. Comparative analysis revealed distinctly designed ID loops in each GLTP family member. This analysis also disclosed a conserved H-bond triplet that "clasps" both ID-loop ends together to promote structural autonomy and rigidity. The findings indicated that various ID loops work in concert with conserved recognition centers to create different specificities among family members. We also observed four bulky, conserved hydrophobic residues involved in "sensor-like" interactions with lipid chains in protein hydrophobic pockets and FF motifs in GLTP and FAPP2, well-positioned to provide acyl chain-dependent SL selectivity for the hydrophobic pockets. In summary, our study provides mechanistic insights into sphingolipid recognition by the GLTP fold and uncovers the elements involved in this recognition.

Roles of exosome-associated glycosphingolipids in immune tolerance of embryo implantation and pregnancy

Establishment of pregnancy requires synchronized growth between the endometrium and the blastocyst. Functional interaction between these occurs both during the pre-implantation phase of embryo implantation and during placentation. Pregnancy is a unique event in which a fetus, despite being genetically and immunologically different from the mother, develops in the uterus. Successful pregnancy implies avoidance of rejection by the maternal immune system. Exosomes released from the endometrium and the embryo are present in uterine fluid. These can transfer miRNA,mRNAs, proteins and lipids between cells, thus providing endometrial-embryo communication in the peri-implantation period. Exosomes have been considered of critical importance for embryo implantation and programming of human pregnancy. In the present study, we examined that the action of glycosphingolipids (GSLs) in exosomes, and their role as preventing the embryo from being attacked by the maternal immune system. In this in vitro study, we examined whether GSLs could be purified from exosomes derived from abortus villi. To demonstrate the immunomodulatory capacity of exosomes. To test macrophage M1/M2 polarization, indicating the role of exosomes in embryo implantation and pregnancy. Human villus trophoblast cells were isolated from the abortus tissue from healthy women undergoing pregnancy termination of a pregnancy at 6- to 12-wk gestation, after informed consent. GSLs transfected from exosomes to monocytes. Macrophage M1/M2 polarization was tested by flow cytometry with CD68/CD80/CD163 markers. Transmission electron microscopy (TEM) images of isolated exosomes were performed. GSLs were successfully transfected from exosomes to monocytes. Pretreatment with exosomes significantly induced macrophage M2 polarization. Moreover, isolated exosomes from villus trophoblast cells were confirmed by transmission electron microscopy images. Pretreatment with exosomes derived from villus trophoblast cells of a normal pregnancy significantly induced macrophage M2 polarization compared with anembryonic pregnancy through M1 macrophage marker expression by qRT-PCR. Our results demonstrate that GSLs were significant expressed in exosomes derived from villus trophoblast cells, indicating the GSLs have potential modulatory role on embryo implantation and decidual programming of human pregnancy. This study demonstrates that exosomes derived from villus trophoblast cells of a normal pregnancy significantly induced macrophage M2 polarization. Our findings represent a new concept regarding the immunomodulatory capacity of exosomes from embryos and villi, suggesting that exosomes have potential modulatory role on embryo implantation and decidual programming of human pregnancy.

\u03b1-Synuclein interacts directly but reversibly with psychosine: implications for \u03b1-synucleinopathies

Aggregation of α-synuclein, the hallmark of α-synucleinopathies such as Parkinson’s disease, occurs in various glycosphingolipidoses. Although α-synuclein aggregation correlates with deficiencies in the lysosomal degradation of glycosphingolipids (GSL), the mechanism(s) involved in this aggregation remains unclear. We previously described the aggregation of α-synuclein in Krabbe’s disease (KD), a neurodegenerative glycosphingolipidosis caused by lysosomal deficiency of galactosyl-ceramidase (GALC) and the accumulation of the GSL psychosine. Here, we used a multi-pronged approach including genetic, biophysical and biochemical techniques to determine the pathogenic contribution, reversibility, and molecular mechanism of aggregation of α-synuclein in KD. While genetic knock-out of α-synuclein reduces, but does not completely prevent, neurological signs in a mouse model of KD, genetic correction of GALC deficiency completely prevents α-synuclein aggregation. We show that psychosine forms hydrophilic clusters and binds the C-terminus of α-synuclein through its amino group and sugar moiety, suggesting that psychosine promotes an open/aggregation-prone conformation of α-synuclein. Dopamine and carbidopa reverse the structural changes of psychosine by mediating a closed/aggregation-resistant conformation of α-synuclein. Our results underscore the therapeutic potential of lysosomal correction and small molecules to reduce neuronal burden in α-synucleinopathies, and provide a mechanistic understanding of α-synuclein aggregation in glycosphingolipidoses.

Membrane assembly of Shiga toxin glycosphingolipid receptors and toxin refractiveness of MDCK II epithelial cells

Shiga toxins (Stxs) are the major virulence factors of Stx-producing Escherichia coli (STEC), which cause hemorrhagic colitis and severe extraintestinal complications due to injury of renal endothelial cells, resulting in kidney failure. Since kidney epithelial cells are suggested additional targets for Stxs, we analyzed Madin-Darby canine kidney (MDCK) II epithelial cells for presence of Stx-binding glycosphingolipids (GSLs), determined their distribution to detergent-resistant membranes (DRMs), and ascertained the lipid composition of DRM and non-DRM preparations. Globotriaosylceramide and globotetraosylceramide, known as receptors for Stx1a, Stx2a, and Stx2e, and Forssman GSL as a specific receptor for Stx2e, were found to cooccur with SM and cholesterol in DRMs of MDCK II cells, which was shown using TLC overlay assay detection combined with mass spectrometry. The various lipoforms of GSLs were found to mainly harbor ceramide moieties composed of sphingosine (d18:1) and C24:1/C24:0 or C16:0 FA. The cells were highly refractory toward Stx1a, Stx2a, and Stx2e, most likely due to the absence of Stx-binding GSLs in the apical plasma membrane determined by immunofluorescence confocal laser scanning microscopy. The results suggest that the cellular content of Stx receptor GSLs and their biochemical detection in DRM preparations alone are inadequate to predict cellular sensitivity toward Stxs.

Intact glycosphingolipidomic analysis of the cell membrane during differentiation yields extensive glycan and lipid changes

Glycosphingolipids (GSLs) are found in cellular membranes of most organisms and play important roles in cell-cell recognition, signaling, growth, and adhesion, among others. A method based on nanoflow high performance liquid chromatography-chip-quadrupole-time-of-flight mass spectrometry (nanoHPLC Chip-Q-TOF MS) was applied towards identifying and quantifying intact GSLs from a variety of samples, including cultured cell lines and animal tissue. The method provides the composition and sequence of the glycan, as well as variations in the ceramide portion of the GSL. It was used to profile the changes in the glycolipidome of Caco-2 cells as they undergo differentiation. A total of 226 unique GSLs were found among Caco-2 samples from five differentiation time-points. The method provided a comprehensive glycolipidomic profile of a cell during differentiation to yield the dynamic variation of intact GSL structures.

Synthetic Strategies for Modified Glycosphingolipids and Their Design as Probes.

The plasma membrane of cells contains a diverse array of lipids that provide important structural and biological features. Glycolipids are typically a minor component of the cell membrane and consist primarily of glycosphingolipids (GSLs). GSLs in vertebrates contain a multifarious assortment of glycan headgroups, which can be important to biological functions based on lipid-lipid and lipid-protein interactions. The design of probes to study these complex targets requires advanced synthetic methodologies. In this Review, we will discuss recent advances in chemical and chemoenzymatic synthesis of GSLs in conjunction with the use of these approaches to design new probes. Examples using either chemical or enzymatic semisynthesis methods starting from isolated GSLs will also be reviewed. Focusing primarily on vertebrate glycolipids, we will highlight examples of radionuclide, fluorophore, photoresponsive, and bioorthogonal tagged GSL probes.

Abstract 5772: Engineered lectins to treat cancer

Abstract Targeted delivery of cytotoxic compounds to tumors has become one of the most dynamic areas of research and development in the cancer therapy field. In this context, glycosphingolipids (GSLs) represent a promising class of tumor markers. Indeed, cancer patients have altered GSL expression patterns on their tumoral cells compared to healthy tissue (Krengel et al., 2014). In a recent prioritization of cancer antigens by the National Cancer Institute at Rockville (USA), 4 out of 75 were GSLs (GD2, GD3, fucosyl-GM1, and GM3), with GD2 arriving already at the 12th position (Cheever et al., 2009). However, GSLs are only rarely addressed in the context of tumor targeting, obtaining GSL specific antibodies being a notorious difficult task. An exception is the anti-GD2 antibody, dinutuximab, which entered the market for the treatment of high-risk neuroblastoma patients, which is unfortunately associated to dose-limiting acute toxicity (Yu et al., 2010). This project aims at developing a novel class of therapeutic products for the delivery of therapeutic compounds by targeting tumor-specific GSLs. Our products are based on a naturally occurring GSL-binding lectin with intrinsic tumor targeting capacity. We will rely on a proprietary technology to derive products which are tuned to transport cytotoxic compounds specifically into cancer cells. As a proof of concept, we apply our technology to a tumor-specific GSL, GD2, to generate a therapeutic formulation against neuroblastoma, one of the most frequent cancer in children under 5 years old. Our technology has truly groundbreaking potential as, in principle, it can apply to any GSL to specifically target several common tumors. Citation Format: Thomas Murarasu, Ludger Johannes. Engineered lectins to treat cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5772.

Emerging concepts of ganglioside metabolism.

Gangliosides (GGs) are sialic acid-containing glycosphingolipids (GSLs) and major membrane components enriched on cellular surfaces. Biosynthesis of mammalian GGs starts at the cytosolic leaflet of endoplasmic reticulum (ER) membranes with the formation of their hydrophobic ceramide anchors. After intracellular ceramide transfer to Golgi and trans-Golgi network (TGN) membranes, anabolism of GGs, as well as of other GSLs, is catalyzed by membrane-spanning glycosyltransferases (GTs) along the secretory pathway. Combined activity of only a few promiscuous GTs allows for the formation of cell-type-specific glycolipid patterns. Following an exocytotic vesicle flow to the cellular plasma membranes, GGs can be modified by metabolic reactions at or near the cellular surface. For degradation, GGs are endocytosed to reach late endosomes and lysosomes. Whereas membrane-spanning enzymes of the secretory pathway catalyze GSL and GG formation, a cooperation of soluble glycosidases, lipases and lipid-binding cofactors, namely the sphingolipid activator proteins (SAPs), act as the main players of GG and GSL catabolism at intralysosomal luminal vesicles (ILVs).

Biological Roles Played by Sphingolipids in Dimorphic and Filamentous Fungi.

ABSTRACTFilamentous and dimorphic fungi cause invasive mycoses associated with high mortality rates. Among the fungal determinants involved in the establishment of infection, glycosphingolipids (GSLs) have gained increased interest in the last few decades. GSLs are ubiquitous membrane components that have been isolated from both filamentous and dimorphic species and play a crucial role in polarized growth as well as hypha-to-yeast transition. In fungi, two major classes of GSLs are found: neutral and acidic GSLs. Neutral GSLs comprise glucosylceramide and galactosylceramide, which utilize Δ4-Δ8-9-methyl-sphingadienine as a sphingoid base, linked to a C16–18 fatty acid chain, forming ceramide, and to a sugar residue, such as glucose or galactose. In contrast, acidic GSLs include glycosylinositol phosphorylceramides (GIPCs), composed of phytosphingosine attached to a long or very long fatty acid chain (C18–26) and to diverse and complex glycan groups via an inositol-phosphate linker. GIPCs are absent in mammalian cells, while fungal glucosylceramide and galactosylceramide are present but diverge structurally from their counterparts. Therefore, these compounds and their biosynthetic pathways represent potential targets for the development of selective therapeutic strategies. In this minireview, we discuss the enzymatic steps involved in the production of fungal GSLs, analyze their structure, and address the role of the currently characterized genes in the biology and pathogenesis of filamentous and dimorphic fungi.