Blockade of Glycosphingolipid Synthesis Inhibits Cell Cycle and Spheroid Growth of Colon Cancer Cells In Vitro and Experimental Colon Cancer Incidence In Vivo

Colorectal cancer (CRC) is one of the most frequently diagnosed cancers in humans. At early stages CRC is treated by surgery and at advanced stages combined with chemotherapy. We examined here the potential effect of glucosylceramide synthase (GCS)-inhibition on CRC biology. GCS is the rate-limiting enzyme in the glycosphingolipid (GSL)-biosynthesis pathway and overexpressed in many human tumors. We suppressed GSL-biosynthesis using the GCS inhibitor Genz-123346 (Genz), NB-DNJ (Miglustat) or by genetic targeting of the GCS-encoding gene UDP-glucose-ceramide-glucosyltransferase- (UGCG). GCS-inhibition or GSL-depletion led to a marked arrest of the cell cycle in Lovo cells. UGCG silencing strongly also inhibited tumor spheroid growth in Lovo cells and moderately in HCT116 cells. MS/MS analysis demonstrated markedly elevated levels of sphingomyelin (SM) and phosphatidylcholine (PC) that occurred in a Genz-concentration dependent manner. Ultrastructural analysis of Genz-treated cells indicated multi-lamellar lipid storage in vesicular compartments. In mice, Genz lowered the incidence of experimentally induced colorectal tumors and in particular the growth of colorectal adenomas. These results highlight the potential for GCS-based inhibition in the treatment of CRC.

ATP-binding cassette transporters mediate differential biosynthesis of glycosphingolipid species

The cytosolic-oriented glucosylceramide (GlcCer) synthase is enigmatic, requiring nascent GlcCer translocation to the luminal Golgi membrane to access glycosphingolipid (GSL) anabolic glycosyltransferases. The mechanism by which GlcCer is flipped remains unclear. To investigate the role of GlcCer-binding partners in this process, we previously made cleavable, biotinylated, photoreactive GlcCer analogs in which the reactive nitrene was closely apposed to the GlcCer head group, while maintaining a C16-acyl chain. GlcCer-binding protein specificity was validated for both photoprobes. Using one probe, XLB, here we identified ATP-binding cassette (ABC) transporters ABCA3, ABCB4, and ABCB10 as unfractionated microsomal GlcCer-binding proteins in DU-145 prostate tumor cells. siRNA knockdown (KD) of these transporters differentially blocked GSL synthesis assessed in toto and via metabolic labeling. KD of ABCA3 reduced acid/neutral GSL levels, but increased those of LacCer, while KD of ABCB4 preferentially reduced neutral GSL levels, and KD of ABCB10 reduced levels of both neutral and acidic GSLs. Depletion of ABCA12, implicated in GlcCer transport, preferentially decreased neutral GSL levels, while ABCB1 KD preferentially reduced gangliosides, but increased neutral GSL Gb3. These results imply that multiple ABC transporters may provide distinct but overlapping GlcCer and LacCer pools within the Golgi lumen for anabolism of different GSL series by metabolic channeling. Differential ABC family member usage may fine-tune GSL biosynthesis depending on cell/tissue type. We conclude that ABC transporters provide a new tool for the regulation of GSL biosynthesis and serve as potential targets to reduce selected GSL species/subsets in diseases in which GSLs are dysregulated.

Lyso-glycosphingolipids: presence and consequences

Lyso-glycosphingolipids are generated in excess in glycosphingolipid storage disorders. In the course of these pathologies glycosylated sphingolipid species accumulate within lysosomes due to flaws in the respective lipid degrading machinery. Deacylation of accumulating glycosphingolipids drives the formation of lyso-glycosphingolipids. In lysosomal storage diseases such as Gaucher Disease, Fabry Disease, Krabbe disease, GM1 -and GM2 gangliosidosis, Niemann Pick type C and Metachromatic leukodystrophy massive intra-lysosomal glycosphingolipid accumulation occurs. The lysosomal enzyme acid ceramidase generates the deacylated lyso-glycosphingolipid species. This review discusses how the various lyso-glycosphingolipids are synthesized, how they may contribute to abnormal immunity in glycosphingolipid storing lysosomal diseases and what therapeutic opportunities exist.

Proteins involved in the biosynthesis of lipophosphoglycan in Leishmania: a comparative genomic and evolutionary analysis

BACKGROUND

Leishmania spp. are digenetic parasites capable of infecting humans and causing a range of diseases collectively known as leishmaniasis. The main mechanisms involved in the development and permanence of this pathology are linked to evasion of the immune response. Crosstalk between the immune system and particularities of each pathogenic species is associated with diverse disease manifestations. Lipophosphoglycan (LPG), one of the most important molecules present on the surface of Leishmania parasites, is divided into four regions with high molecular variability. Although LPG plays an important role in host-pathogen and vector-parasite interactions, the distribution and phylogenetic relatedness of the genes responsible for its synthesis remain poorly explored. The recent availability of full genomes and transcriptomes of Leishmania parasites offers an opportunity to leverage insight on how LPG-related genes are distributed and expressed by these pathogens.

RESULTS

Using a phylogenomics-based framework, we identified a catalog of genes involved in LPG biosynthesis across 22 species of Leishmania from the subgenera Viannia and Leishmania, as well as 5 non-Leishmania trypanosomatids. The evolutionary relationships of these genes across species were also evaluated. Nine genes related to the production of the glycosylphosphatidylinositol (GPI)-anchor were highly conserved among compared species, whereas 22 genes related to the synthesis of the repeat unit presented variable conservation. Extensive gain/loss events were verified, particularly in genes SCG1-4 and SCA1-2. These genes act, respectively, on the synthesis of the side chain attached to phosphoglycans and in the transfer of arabinose residues. Phylogenetic analyses disclosed evolutionary patterns reflective of differences in host specialization, geographic origin and disease manifestation.

CONCLUSIONS

The multiple gene gain/loss events identified by genomic data mining help to explain some of the observed intra- and interspecies variation in LPG structure. Collectively, our results provide a comprehensive catalog that details how LPG-related genes evolved in the Leishmania parasite specialization process.

Caulobacter crescentus Adapts to Phosphate Starvation by Synthesizing Anionic Glycoglycerolipids and a Novel Glycosphingolipid

Caulobacter crescentus adapts to phosphate starvation by elongating its cell body and a polar stalk structure. The stalk is an extension of the Gram-negative envelope containing inner and outer membranes as well as a peptidoglycan cell wall. Cellular elongation requires a 6- to 7-fold increase in membrane synthesis, yet phosphate limitation would preclude the incorporation of additional phospholipids. In the place of phospholipids, C. crescentus can synthesize several glycolipid species, including a novel glycosphingolipid (GSL-2). While glycosphingolipids are ubiquitous in eukaryotes, the presence of GSL-2 in C. crescentus is surprising since GSLs had previously been found only in Sphingomonas species, in which they play a role in outer membrane integrity. In this paper, we identify three proteins required for GSL-2 synthesis: CcbF catalyzes the first step in ceramide synthesis, while Sgt1 and Sgt2 sequentially glycosylate ceramides to produce GSL-2. Unlike in Sphingomonas, GSLs are nonessential in C. crescentus; however, the presence of ceramides does contribute to phage resistance and susceptibility to the cationic antimicrobial peptide polymyxin B. The identification of a novel lipid species specifically produced upon phosphate starvation suggests that bacteria may be able to synthesize a wider variety of lipids in response to stresses than previously observed. Uncovering these lipids and their functional relevance will provide greater insight into microbial physiology and environmental adaptation.IMPORTANCE Bacteria adapt to environmental changes in a variety of ways, including altering their cell shape. Caulobacter crescentus adapts to phosphate starvation by elongating its cell body and a polar stalk structure containing both inner and outer membranes. While we generally think of cellular membranes being composed largely of phospholipids, cellular elongation occurs when environmental phosphate, and therefore phospholipid synthesis, is limited. In order to adapt to these environmental constraints, C. crescentus synthesizes several glycolipid species, including a novel glycosphingolipid. This finding is significant because glycosphingolipids, while ubiquitous in eukaryotes, are extremely rare in bacteria. In this paper, we identify three proteins required for GSL-2 synthesis and demonstrate that they contribute to phage resistance. These findings suggest that bacteria may synthesize a wider variety of lipids in response to stresses than previously observed.

Tamoxifen inhibits the biosynthesis of inositolphosphorylceramide in Leishmania

Previous work from our group showed that tamoxifen, an oral drug that has been in use for the treatment of breast cancer for over 40 years, is active both in vitro and in vivo against several species of Leishmania, the etiological agent of leishmaniasis. Using a combination of metabolic labeling with [³H]-sphingosine and myo-[³H]-inositol, alkaline hydrolysis, HPTLC fractionations and mass spectrometry analyses, we observed a perturbation in the metabolism of inositolphosphorylceramides (IPCs) and phosphatidylinositols (PIs) after treatment of L. amazonensis promastigotes with tamoxifen, with a significant reduction in the biosynthesis of the major IPCs (composed of d16:1/18:0-IPC, t16:0/C18:0-IPC, d18:1/18:0-IPC and t16:0/20:0-IPC) and PIs (sn-1-O-(C_18:0)alkyl -2-O-(C_18:1)acylglycerol-3-HPO₄-inositol and sn-1-O-(C_18:0)acyl-2-O-(C_18:1)acylglycerol-3-HPO₄-inositol) species. Substrate saturation kinetics of myo-inositol uptake analyses indicated that inhibition of inositol transport or availability were not the main reasons for the reduced biosynthesis of IPC and PI observed in tamoxifen treated parasites. An in vitro enzymatic assay was used to show that tamoxifen was able to inhibit the Leishmania IPC synthase with an IC₅₀ value of 8.48 μM (95% CI 7.68–9.37), suggesting that this enzyme is most likely one of the targets for this compound in the parasites.

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Tamoxifen alters the sphingolipid metabolism of L. amazonensis.

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Tamoxifen treated parasites show a significant reduction of IPC and PI species.

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Tamoxifen-treated parasites present a reduction of inositol transport.

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Tamoxifen is an inhibitor of L. major's IPC synthase in a micromolar range.

Promoter identification and analysis of key glycosphingolipid biosynthesis-globo series pathway genes in piglets

Glycosphingolipid biosynthesis-globo series pathway genes (FUT1, FUT2, ST3GAL1, HEXA, HEXB, B3GALNT1, and NAGA) play an important regulatory role in the defense against Escherichia coli F18 in piglets. In this study, we identified the transcription initiation site and promoter of this gene cluster by mined previous RNA-seq results using bioinformatics tools. The FUT1 transcription initiation region included five alternative splicing sites and two promoter regions, whereas each of the six other genes had one promoter. Dual luciferase reporter results revealed significantly higher transcriptional activity by FUT1 promoter 2, indicating that it played a more important role in transcription. The promoters of glycosphingolipid biosynthesis genes identified contained a CpG island within the first 500 bp, except for the B3GALNT1 promoter which included fewer CpG sites. These results provide a deeper insight into methylation and the regulatory mechanisms of glycosphingolipid biosynthesis-globo series pathway genes in piglets.

Evaluation of an amino acid residue critical for the specificity and activity of human Gb3/CD77 synthase

Human Gb3/CD77 synthase (α1,4-galactosyltransferase) is the only known glycosyltransferase that changes acceptor specificity because of a point mutation. The enzyme, encoded by A4GALT locus, is responsible for biosynthesis of Gal(α1-4)Gal moiety in Gb3 (CD77, P^k antigen) and P1 glycosphingolipids. We showed before that a single nucleotide substitution c.631C > G in the open reading frame of A4GALT, resulting in replacement of glutamine with glutamic acid at position 211 (substitution p. Q211E), broadens the enzyme acceptor specificity, so it can not only attach galactose to another galactose but also to N-acetylgalactosamine. The latter reaction leads to synthesis of NOR antigens, which are glycosphingolipids with terminal Gal(α1-4)GalNAc sequence, never before described in mammals. Because of the apparent importance of position 211 for enzyme activity, we stably transfected the 2102Ep cells with vectors encoding Gb3/CD77 synthase with glutamine substituted by aspartic acid or asparagine, and evaluated the cells by quantitative flow cytometry, high-performance thin-layer chromatography and real-time PCR. We found that cells transfected with vectors encoding Gb3/CD77 synthase with substitutions p. Q211D or p. Q211N did not express P^k, P1 and NOR antigens, suggesting complete loss of enzymatic activity. Thus, amino acid residue at position 211 of Gb3/CD77 synthase is critical for specificity and activity of the enzyme involved in formation of P^k, P1 and NOR antigens. Altogether, this approach affords a new insight into the mechanism of action of the human Gb3/CD77 synthase.

Glycosphingolipid synthesis inhibition limits osteoclast activation and myeloma bone disease

Glycosphingolipids (GSLs) are essential constituents of cell membranes and lipid rafts and can modulate signal transduction events. The contribution of GSLs in osteoclast (OC) activation and osteolytic bone diseases in malignancies such as the plasma cell dyscrasia multiple myeloma (MM) is not known. Here, we tested the hypothesis that pathological activation of OCs in MM requires de novo GSL synthesis and is further enhanced by myeloma cell-derived GSLs. Glucosylceramide synthase (GCS) inhibitors, including the clinically approved agent N-butyl-deoxynojirimycin (NB-DNJ), prevented OC development and activation by disrupting RANKL-induced localization of TRAF6 and c-SRC into lipid rafts and preventing nuclear accumulation of transcriptional activator NFATc1. GM3 was the prevailing GSL produced by patient-derived myeloma cells and MM cell lines, and exogenous addition of GM3 synergistically enhanced the ability of the pro-osteoclastogenic factors RANKL and insulin-like growth factor 1 (IGF-1) to induce osteoclastogenesis in precursors. In WT mice, administration of GM3 increased OC numbers and activity, an effect that was reversed by treatment with NB-DNJ. In a murine MM model, treatment with NB-DNJ markedly improved osteolytic bone disease symptoms. Together, these data demonstrate that both tumor-derived and de novo synthesized GSLs influence osteoclastogenesis and suggest that NB-DNJ may reduce pathological OC activation and bone destruction associated with MM.

Deletion of PdMit1, a homolog of yeast Csg1, affects growth and Ca(2+) sensitivity of the fungus Penicillium digitatum, but does not alter virulence

GDP-mannose:inositol-phosphorylceramide (MIPC) and its derivatives are important for Ca(2+) sensitization of Saccharomyces cerevisiae and for the virulence of Candida albicans, but its role in the virulence of plant fungal pathogens remains unclear. In this study, we report the identification and functional characterization of PdMit1, the gene encoding MIPC synthase in Penicillium digitatum, one of the most important pathogens of postharvest citrus fruits. To understand the function of PdMit1, a PdMit1 deletion mutant was generated. Compared to its wild-type control, the PdMit1 deletion mutant exhibited slow radial growth, decreased conidia production and delayed conidial germination, suggesting that PdMit1 is important for the growth of mycelium, sporulation and conidial germination. The PdMit1 deletion mutant also showed hypersensitivity to Ca(2+). Treatment with 250 mmol/l Ca(2+) induced vacuole fusion in the wild-type strain, but not in the PdMit1 deletion mutant. Treatment with 250mmol/lCaCl2 upregulated three Ca(2+)-ATPase genes in the wild-type strain, and this was significantly inhibited in the PdMit1 deletion mutant. These results suggest that PdMit1 may have a role in regulating vacuole fusion and expression of Ca(2+)-ATPase genes by controlling biosynthesis of MIPC, and thereby imparts P. digitatum Ca(2+) tolerance. However, we found that PdMit1 is dispensable for virulence of P. digitatum.

Human genetic disorders of sphingolipid biosynthesis

Monogenic defects of sphingolipid biosynthesis have been recently identified in human patients. These enzyme deficiencies affect the synthesis of sphingolipid precursors, ceramides or complex glycosphingolipids. They are transmitted as autosomal recessive or dominant traits, and their resulting phenotypes often replicate the abnormalities seen in murine models deficient for the corresponding enzymes. In quite good agreement with the known critical roles of sphingolipids in cells from the nervous system and the epidermis, these genetic defects clinically manifest as neurological disorders, including paraplegia, epilepsy or peripheral neuropathies, or present with ichthyosis. The present review summarizes the genetic alterations, biochemical changes and clinical symptoms of this new group of inherited metabolic disorders. Hypotheses regarding the molecular pathophysiology and potential treatments of these diseases are also discussed.

The design and clinical development of inhibitors of glycosphingolipid synthesis: will invention be the mother of necessity?

The treatment of glycosphingolipid storage diseases by synthesis inhibition was first proposed 40 years ago as an alternative approach to enzyme replacement therapy. We have pursued this strategy through the rational design of potent and selective inhibitors of glucosylceramide synthase, the first step in glycosphingolipid synthesis. Eliglustat tartrate was the result of these efforts and is currently the focus of phase 3 trials for type 1 Gaucher disease. Phase 2 studies showed a reduction in splenomegaly and hepatomegaly and improvements of anemia and thrombocytopenia at levels equivalent to or exceeding the historic response to imiglucerase. Structural analogues of eliglustat have also been designed that lack pgp-1 recognition and cross the blood brain barrier. These may have utility for central nervous system- based sphingolipidoses. Because glycosphingolipids are important regulators of receptor tyrosine kinases, glucosylceramide synthase inhibitors may also be beneficial for disorders such as type 2 diabetes mellitus and polycystic kidney disease.

Lipidomics of Candida albicans biofilms reveals phase-dependent production of phospholipid molecular classes and role for lipid rafts in biofilm formation

Candida albicans-associated bloodstream infections are linked to the ability of this yeast to form biofilms. In this study, we used lipidomics to compare the lipid profiles of C. albicans biofilms and planktonic cells, in early and mature developmental phases. Our results showed that significant differences exist in lipid composition in both developmental phases. Biofilms contained higher levels of phospholipid and sphingolipids than planktonic cells (nmol per g biomass, P<0.05 for all comparisons). In the early phase, levels of lipid in most classes were significantly higher in biofilms compared to planktonic cells (P≤0.05). The ratio of phosphatidylcholine to phosphatidylethanolamine was lower in biofilms compared to planktonic cells in both early (1.17 vs 2.52, P≤0.001) and late (2.34 vs 3.81, P≤0.001) developmental phases. The unsaturation index of phospholipids decreased with time, with this effect being particularly strong for biofilms. Inhibition of the biosynthetic pathway for sphingolipid [mannosyl diinositolphosphoryl ceramide, M(IP)₂C] by myriocin or aureobasidin A, and disruption of the gene encoding inositolphosphotransferase (Ipt1p), abrogated the ability of C. albicans to form biofilms. The differences in lipid profiles between biofilms and planktonic Candida cells may have important implications for the biology and antifungal resistance of biofilms.

Inhibition of glycosphingolipid biosynthesis induces cytokinesis failure

Although cells undergo dramatic shape changes during cytokinesis, the role of the plasma membrane and lipids is poorly understood. We report that inactivation of glucosyl ceramide synthase (GCS), either by RNAi or with the small molecule PPMP, causes failure of cleavage furrow ingression. Using mass-spectrometry-based global lipid profiling, we identify individual lipids that are enhanced or depleted due to GCS inhibition. We show that GCS inhibition results in the mislocalization of actin and the ERM proteins, key cytoskeletal proteins that connect the plasma membrane to the actin cortex. Our data suggest that ceramides participate in mediating the interactions between the membrane and the cortex.

UV-MALDI mass spectrometry analysis of NBD-glycosphingolipids without an external matrix

Each day, advances in the instrumentation and operating protocols bring new applications and insights into the molecular processes of ultra violet-matrix assisted laser desorption/ionization-mass spectrometry (UV-MALDI MS), increasing its potential use. We report here an approach in which mass spectrometry analysis of sphingolipids has been performed using a fluorescent tag (nitrobenz-2-oxa-1, 3-diazole, NBD) covalently linked to the sphingoid base as matrix. Thus, different labeled-sphingolipids were analyzed: ceramide, dihydroceramide, acetylceramide, glucosylceramide, galactosylceramide, galactosyldihydroceramide. In addition an extract of glycosphingolipids obtained from epimastigote forms of Trypanosoma cruzi metabolically labeled with NBD-ceramide was analyzed. The goal of this work is to show that no matrix needs to be added for the mass spectrometry analysis as the same tag used to label the lipids may generate efficiently analyte ions to obtain high quality signals.

High incidence of GalNAc disialosyl lactotetraosylceramide in metastatic renal cell carcinoma

BACKGROUND

In renal cell carcinoma (RCC), glycosphingolipids monosialosyl globopentaosylceramide (MSGb5) and GalNAc disialosyl lactotetraosylceramide (GaINAcDSLc4) were shown to be predictors of metastasis. Here we extended the research using a larger cohort of patients with a longer follow-up period, and reevaluate their relationship to malignant potential, metastasis and prognosis in patients with RCC.

PATIENTS AND METHODS

MSGb5 and GalNAcDSLc4 were examined in 114 primary RCCs by immunohistochemical method on cryostat sections.

RESULTS

GalNAcDSLc4 was detected in 13.2% of RCCs and was associated with a significantly higher incidence of metastasis at the time of primary visit (60.0% vs. 31.3%, p=0.0419) as well as de novo metastasis during followup (33.3% vs. 14.7%), and a shorter survival (p=0.0399). MSGb5 was detected in 51.8% of tumors and was not related to clinocopathological characteristics or survival.

CONCLUSION

RCC patients with tumors positive for GalNAcDSLc4 are at higher risk of metastasis at the time of diagnosis and during follow-up.

Distinct contributions of β4GalNAcTA and β4GalNAcTB to Drosophila glycosphingolipid biosynthesis

Drosophila melanogaster has two beta4-N-acetylgalactosaminyltransferases, beta4GalNAcTA and beta4GalNAcTB, that are able to catalyse the formation of lacdiNAc (GalNAcbeta,4GlcNAc). LacdiNAc is found as a structural element of Drosophila glycosphingolipids (GSLs) suggesting that beta4GalNAcTs contribute to the generation of GSL structures in vivo. Mutations in Egghead and Brainaic, enzymes that generate the beta4GalNAcT trisaccharide acceptor structure GlcNAcbeta,3Manbeta,4GlcbetaCer, are lethal. In contrast, flies doubly mutant for the beta4GalNAcTs are viable and fertile. Here, we describe the structural analysis of the GSLs in beta4GalNAcT mutants and find that in double mutant flies no lacdiNAc structure is generated and the trisaccharide GlcNAcbeta,3Manbeta,4GlcbetaCer accumulates. We also find that phosphoethanolamine transfer to GlcNAc in the trisaccharide does not occur, demonstrating that this step is dependent on prior or simultaneous transfer of GalNAc. By comparing GSL structures generated in the beta4GalNAcT single mutants we show that beta4GalNAcTB is the major enzyme for the overall GSL biosynthesis in adult flies. In beta4GalNAcTA mutants, composition of GSL structures is indistinguishable from wild-type animals. However, in beta4GalNAcTB mutants precursor structures are accumulating in different steps of GSL biosynthesis, without the complete loss of lacdiNAc, indicating that beta4GalNAcTA plays a minor role in generating GSL structures. Together our results demonstrate that both beta4GalNAcTs are able to generate lacdiNAc structures in Drosophila GSL, although with different contributions in vivo, and that the trisaccharide GlcNAcbeta,3Manbeta,4GlcbetaCer is sufficient to avoid the major phenotypic consequences associated with the GSL biosynthetic defects in Brainiac or Egghead.

Human umbilical cord-derived cells can often serve as feeder cells to maintain primate embryonic stem cells in a state capable of producing hematopoietic cells

Clinical application of human embryonic stem (ES) cells will require the establishment of methods for their culture, either in the presence or absence of human-derived feeder cells. We have tested the ability of non-immortalized cultured cells derived from human umbilical cord (HUC cells) to support ES cell culture. A primate ES cell line that had been established and maintained with mouse embryonic fibroblasts was cultured on HUC cells for >3 months (HUC-maintained ES cells). These cells retained their expression of alkaline phosphatase, SSEA-4, Oct-3/4, and to a lesser extent Nanog, but did not express Rex-1. Nevertheless, HUC-maintained ES cells could produce ectoderm-, mesoderm- and endoderm-derived cells in teratomata that they formed in immunodeficient mice. We show that HUC-maintained ES cells could give rise to hematopoietic cells, although this ability of HUC cells varied among HUC cell populations derived from different neonates. HUC cells are promising as human material with which to maintain ES cells in a state that retains their ability to produce mature cells, including hematopoietic cells.

Glycosphingolipid synthesis requires FAPP2 transfer of glucosylceramide

The molecular machinery responsible for the generation of transport carriers moving from the Golgi complex to the plasma membrane relies on a tight interplay between proteins and lipids. Among the lipid-binding proteins of this machinery, we previously identified the four-phosphate adaptor protein FAPP2, the pleckstrin homology domain of which binds phosphatidylinositol 4-phosphate and the small GTPase ARF1. FAPP2 also possesses a glycolipid-transfer-protein homology domain. Here we show that human FAPP2 is a glucosylceramide-transfer protein that has a pivotal role in the synthesis of complex glycosphingolipids, key structural and signalling components of the plasma membrane. The requirement for FAPP2 makes the whole glycosphingolipid synthetic pathway sensitive to regulation by phosphatidylinositol 4-phosphate and ARF1. Thus, by coupling the synthesis of glycosphingolipids with their export to the cell surface, FAPP2 emerges as crucial in determining the lipid identity and composition of the plasma membrane.

A specific and potent inhibitor of glucosylceramide synthase for substrate inhibition therapy of Gaucher disease

An approach to treating Gaucher disease is substrate inhibition therapy which seeks to abate the aberrant lysosomal accumulation of glucosylceramide. We have identified a novel inhibitor of glucosylceramide synthase (Genz-112638) and assessed its activity in a murine model of Gaucher disease (D409V/null). Biochemical characterization of Genz-112638 showed good potency (IC(50) approximately 24nM) and specificity against the target enzyme. Mice that received drug prior to significant accumulation of substrate (10 weeks of age) showed reduced levels of glucosylceramide and number of Gaucher cells in the spleen, lung and liver when compared to age-matched control animals. Treatment of older mice that already displayed significant amounts of tissue glucosylceramide (7 months old) resulted in arrest of further accumulation of the substrate and appearance of additional Gaucher cells in affected organs. These data indicate that substrate inhibition therapy with Genz-112638 represents a viable alternate approach to enzyme therapy to treat the visceral pathology in Gaucher disease.

Synthesis of fluorescent glycosphingolipids and neoglycoconjugates which contain 6-gala oligosaccharides using the transglycosylation reaction of a novel endoglycoceramidase (EGALC)

Endoglycoceramidase is a glycohydrolase capable of hydrolysing the O-glycosidic linkage between oligosaccharides and ceramides of various glycosphingolipids. However, no endoglycoceramidase reported so far can hydrolyse 6-gala series glycosphingolipids which possess the common structure R-Gal beta1-6Gal beta1-1'Cer. Recently, we found a novel endoglycoceramidase (endogalactosylceramidase, EGALC) which specifically hydrolyses 6-gala series glycosphingolipids. Here, we report that EGALC catalyses the hydrolysis as well as transglycosylation. An intact sugar chain of neogalatriaosylceramide (Gal beta1-6Gal beta1-6Gal beta1-1'Cer) was found to be transferred by EGALC to a primary hydroxyl group of various alkanols and non-ionic detergents such as Triton X-100 generating corresponding alkyl- and Triton-trigalactooligosaccharides. Furthermore, fluorescent 6-gala series glycosphingolipids were synthesized by transglycosylation in a reaction with EGALC using fluorescent ceramides as acceptors. Because of high efficiency and broad acceptor specificity, EGALC would facilitate the synthesis of fluorescent glycosphingolipids and neoglycoconjugates which contain 6-gala oligosaccharides.

Two functionally divergent UDP-Gal nucleotide sugar transporters participate in phosphoglycan synthesis in Leishmania major

In the protozoan parasite Leishmania, abundant surface and secreted molecules, such as lipophosphoglycan (LPG) and proteophosphoglycans (PPGs), contain extensive galactose in the form of phosphoglycans (PGs) based on (Gal-Man-PO(4)) repeating units. PGs are synthesized in the parasite Golgi apparatus and require transport of cytoplasmic nucleotide sugar precursors to the Golgi lumen by nucleotide sugar transporters (NSTs). GDP-Man transport is mediated by the LPG2 gene product, and here we focused on transporters for UDP-Gal. Data base mining revealed 12 candidate NST genes in the L. major genome, including LPG2 as well as a candidate endoplasmic reticulum UDP-glucose transporter (HUT1L) and several pseudogenes. Gene knock-out studies established that two genes (LPG5A and LPG5B) encoded UDP-Gal NSTs. Although the single lpg5A(-) and lpg5B(-) mutants produced PGs, an lpg5A(-)/5B(-) double mutant was completely deficient. PG synthesis was restored in the lpg5A(-)/5B(-) mutant by heterologous expression of the human UDP-Gal transporter, and heterologous expression of LPG5A and LPG5B rescued the glycosylation defects of the mammalian Lec8 mutant, which is deficient in UDP-Gal uptake. Interestingly, the LPG5A and LPG5B functions overlap but are not equivalent, since the lpg5A(-) mutant showed a partial defect in LPG but not PPG phosphoglycosylation, whereas the lpg5B(-) mutant showed a partial defect in PPG but not LPG phosphoglycosylation. Identification of these key NSTs in Leishmania will facilitate the dissection of glycoconjugate synthesis and its role(s) in the parasite life cycle and further our understanding of NSTs generally.

Stem cells derived from human fetal membranes display multilineage differentiation potential

The amnion is the inner of two membranes surrounding the fetus. That it arises from embryonic epiblast cells prior to gastrulation suggests that it may retain a reservoir of stem cells throughout pregnancy. We found that human amniotic epithelial cells (hAECs) harvested from term-delivered fetal membranes express mRNA and proteins present in human embryonic stem cells (hESCs), including POU domain, class 5, transcription factor 1; Nanog homeobox; SRY-box 2; and stage-specific embryonic antigen-4. In keeping with possible stem cell-like activity, hAECs were also clonogenic, and primary hAEC cultures could be induced to differentiate into cardiomyocytic, myocytic, osteocytic, adipocytic (mesodermal), pancreatic, hepatic (endodermal), neural, and astrocytic (neuroectodermal) cells in vitro, as defined by phenotypic, mRNA expression, immunocytochemical, and/or ultrastructural characteristics. However, unlike hESCs, hAECs did not form teratomas upon transplantation into severe combined immunodeficiency mice testes. Last, using flow cytometry we have shown that only a very small proportion of primary hAECs contain class IA and class II human leukocyte antigens (HLAs), consistent with a low risk of tissue rejection. However, following differentiation into hepatic and pancreatic lineages, significant proportions of cells contained class IA, but not class II, HLAs. These observations suggest that the term amnion, an abundant and easily accessible tissue, may be a useful source of multipotent stem cells that possess a degree of immune privilege.

Inhibiting glycosphingolipid synthesis improves glycemic control and insulin sensitivity in animal models of type 2 diabetes

Previous reports have shown that glycosphingolipids can modulate the activity of the insulin receptor, and studies in transgenic mice suggest a link between altered levels of various gangliosides and the development of insulin resistance. Here, we show that an inhibitor of glycosphingolipid synthesis can improve glucose control and increase insulin sensitivity in two different diabetic animal models. In the Zucker diabetic fatty rat, the glucosylceramide synthase inhibitor (1R,2R)-nonanoic acid[2-(2',3'-dihydro-benzo [1, 4] dioxin-6'-yl)-2-hydroxy-1-pyrrolidin-1-ylmethyl-ethyl]- amide-l-tartaric acid salt (Genz-123346) lowered glucose and A1C levels and improved glucose tolerance. Drug treatment also prevented the loss of pancreatic beta-cell function normally observed in the Zucker diabetic fatty rat and preserved the ability of the animals to secrete insulin. In the diet-induced obese mouse, treatment with Genz-123346 normalized A1C levels and improved glucose tolerance. Analysis of the phosphorylation state of the insulin receptor and downstream effectors showed increased insulin signaling in the muscles of the treated Zucker diabetic fatty rats and diet-induced obese mice. These results suggest that inhibiting glycosphingolipid synthesis can significantly improve insulin sensitivity and glucose homeostasis and may therefore represent a novel therapeutic approach for the treatment of type 2 diabetes.

Induction of human umbilical cord blood-derived stem cells with embryonic stem cell phenotypes into insulin producing islet-like structure

Success in islet-transplantation-based therapies for type I diabetes, coupled with a worldwide shortage of transplant-ready islets, has motivated efforts to develop renewable sources of islet-replacement tissue. Embryonic stem cells (ESCs) have been successfully induced into insulin producing islet-like structure in several studies. However, the source of the ESCs has presented ethical and technical concerns. Here, we isolated a population of stem cells from human cord blood (UCB), which expressed embryo stage specific maker, SSEA-4, and the multi-potential stem cell marker, Oct4. Subsequently, we successfully induced them into insulin-producing islet-like structures, which co-express insulin and C-peptide. These findings might have a significant potential to advance human UCB derived stem-cell-based therapeutics for diabetes.

Inhibition of Leishmania (Leishmania) amazonensis growth and infectivity by aureobasidin A

OBJECTIVES

To study the effect of aureobasidin A, an inhibitor of inositol phosphorylceramide (IPC) synthase, on Leishmania growth and infectivity.

METHODS

Effects of aureobasidin A were determined for: (i) promastigote growth in axenic culture; (ii) promastigote infectivity in macrophage monolayers; (iii) development of footpad lesions in BALB/c mice; (iv) differentiation of amastigotes into promastigotes.

RESULTS

Aureobasidin A (20 microM) inhibited 90% of Leishmania (Leishmania) amazonensis promastigote growth in axenic culture, but the parasites remained viable, i.e. growth curves returned to normal after aureobasidin A was removed from culture medium. The aureobasidin A IC50 was determined by MTT assay as 4.1 microM for L. (L.) amazonensis promastigotes, 12.6 microM for Leishmania (Leishmania) major and 13.7 microM for Leishmania (Viannia) braziliensis. There was a significant delay in infection when L. (L.) amazonensis promastigotes pre-treated with aureobasidin A were inoculated into BALB/c mouse footpads. When aureobasidin A was added to cultured macrophages infected with amastigotes, the number of infected macrophages was reduced by >90%.

CONCLUSIONS

Aureobasidin A is an interesting pharmacological tool to investigate the effect of lipid metabolism inhibition in Leishmania spp.

Drosophila beta 1,4-N-acetylgalactosaminyltransferase-A synthesizes the LacdiNAc structures on several glycoproteins and glycosphingolipids

The GalNAcbeta1,4GlcNAc (LacdiNAc or LDN) structure is a more common structural feature in invertebrate glycoconjugates when compared with the Galbeta1,4GlcNAc structure. Recently, beta1,4-N-acetylgalactosaminyltransferase (beta4GalNAcT) was identified in some invertebrates including Drosophila. However, the LDN structure has not been reported in Drosophila, and the biological function of LDN remains to be determined. In this study, we examined acceptor substrate specificity of Drosophila beta4GalNAcTA by using some N- and O-glycans on glycoproteins and neutral glycosphingolipids (GSLs). GalNAc was efficiently transferred toward N-glycans, O-glycans, and the arthro-series GSLs. Moreover, we showed that dbeta4GalNAcTA contributed to the synthesis of the LDN structure in vivo. The dbeta4GalNAcTA mRNA was highly expressed in the developmental and adult neuronal tissues. Thus, these results suggest that dbeta4GalNAcTA acts on the terminal GlcNAc residue of some glycans for the synthesis of LDN, and the LDN structure may play a role in the physiological or neuronal development of Drosophila.

New insights into glycosphingolipid functions--storage, lipid rafts, and translocators

Glycosphingolipids are key components of eukaryotic cellular membranes. Through their propensity to form lipid rafts, they are important in membrane transport and signaling. At the cell surface, they are required for caveolar-mediated endocytosis, a process required for the action of many glycosphingolipid-binding toxins. Glycosphingolipids also exist intracellularly, on both leaflets of organelle membranes. It is expected that dissecting the mechanisms of cell pathology seen in the glycosphingolipid storage diseases, where lysosomal glycosphingolipid degradation is defective, will reveal their functions. Disrupted cation gradients in Mucolipidosis type IV disease are interlinked with glycosphingolipid storage, defective rab 7 function, and the activation of autophagy. Relationships between drug translocators and glycosphingolipid synthesis are also discussed. Mass spectrometry of cell lines defective in drug transporters reveal clear differences in glycosphingolipid mass and fatty acid composition. The potential roles of glycosphingolipids in lipid raft formation, endocytosis, and cationic gradients are discussed.

Gangliosides play an important role in the organization of CD82-enriched microdomains

Four-transmembrane-domain proteins of the tetraspanin superfamily are the organizers of specific microdomains at the membrane [TERMs (tetraspanin-enriched microdomains)] that incorporate various transmembrane receptors and modulate their activities. The structural aspects of the organization of TERM are poorly understood. In the present study, we investigated the role of gangliosides in the assembly and stability of TERM. We demonstrated that inhibition of the glycosphingolipid biosynthetic pathway with specific inhibitors of glucosylceramide synthase [NB-DGJ (N-butyldeoxygalactonojirimycin) and PPMP (D-threo-1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol.HCl)] resulted in specific weakening of the interactions involving tetraspanin CD82. Furthermore, ectopic expression of the plasma-membrane-bound sialidase Neu3 in mammary epithelial cells also affected stability of the complexes containing CD82: its association with tetraspanin CD151 was decreased, but the association with EGFR [EGF (epidermal growth factor) receptor] was enhanced. The destabilization of the CD82-containing complexes upon ganglioside depletion correlated with the re-distribution of the proteins within plasma membrane. Importantly, depletion of gangliosides affected EGF-induced signalling only in the presence of CD82. Taken together, our results provide strong evidence that gangliosides play an important role in supporting the integrity of CD82-enriched microdomains. Furthermore, these results demonstrate that the association between different tetraspanins in TERM is controlled by distinct mechanisms and identify Neu3 as a first physiological regulator of the integrity of these microdomains.

Characteristics of two CD75-related cell-surface expressed antigens of human lymphocytes

The structure of cell surface carbohydrates expressed on human leukocytes is dependent on the cell's developmental stage, differentiation, and activation. Although modification of oligosaccharide side chains by sialylation is quite common, antigenic determinants on lymphocytes associated with the presence of sialoglycans are still incompletely defined. In the study presented here, monoclonal antibodies (mAbs) were used to characterize two novel but related cell surface carbohydrate antigens. One antigen, denominated as B8, is largely masked by sialyl residues on most lymphocytes, while it is detectable on the majority of B cells. Treatment with sialidase resulted in the exposure of B8 on the surface of blood cells including lymphocytes. Although the second carbohydrate antigen, C1, was sialidase-sensitive, its molecular properties and cellular distribution place it in close vicinity to B8. B8(+) as well as C1(+) lymphocytes were found predominantly in the mantle zone of secondary follicles of tonsillar tissue. These findings raised the possibility that B8 and C1 are closely related to a category of carbohydrate antigens previously classified as CDw76 (recently assigned to CD75s). MAbs directed against B8 or C1 precipitated 34, 37, 43, and 200kDa glycoproteins from tonsillar lymphocytes, indicating that identical cell surface proteins are associated with both antigens. In contrast to B8, however, the expression of C1 was increased on lymphocytes upon activation. Together the results suggest that CD75-related epitopes are distinct molecular entities which may be exposed on glycoproteins and are differently expressed on lymphocytes.

Reduced inflammatory potential of peritoneal macrophages recruited in mice pretreated with a glycolipid synthesis inhibitor

Integral components of mammalian cell membranes, glycosphingolipids (GSL) reside in specialized plasma membrane microdomains critical for cell signaling. N-alkylated nojirimycins are compounds developed for GSL substrate deprivation therapy, blocking GSL synthesis by specifically inhibiting an essential enzyme, ceramide glucosyltransferase. Peritoneal macrophages recruited in mice pretreated with an inhibitory N-alkylnojirimycin displayed a reduced capacity to release either TNFalpha or interleukin-6 when re-exposed to whole killed E. coli in vitro. Cell viability and protein content were not affected. A nojirimycin analogue without GSL inhibitory capacity had no effect. The results show inhibition of GSL synthesis in vivo by an N-alkylnojirimycin can reduce the response to an inflammatory stimulus and indicate N-alkylnojirimycins have experimental and potential clinical value for modulating innate immune responses in vivo.

Glycolipid receptor depletion as an approach to specific antimicrobial therapy

Mucosal pathogens recognize glycoconjugate receptors at the site of infection, and attachment is an essential first step in disease pathogenesis. Inhibition of attachment may prevent disease, and several approaches have been explored. This review discusses the prevention of bacterial attachment and disease by agents that modify the glycosylation of cell surface glycoconjugates. Glycosylation inhibitors were tested in the urinary tract infection model, where P-fimbriated Escherichia coli rely on glycosphingolipid receptors for attachment and tissue attack. N-butyldeoxynojirimycin blocked the expression of glucosylceramide-derived glycosphingolipids and attachment was reduced. Bacterial persistence in the kidneys was impaired and the inflammatory response was abrogated. N-butyldeoxynojirimycin was inactive against strains which failed to engage these receptors, including type 1 fimbriated or nonadhesive strains. In vivo attachment has been successfully prevented by soluble receptor analogues, but there is little clinical experience of such inhibitors. Large-scale synthesis of complex carbohydrates, which could be used as attachment inhibitors, remains a technical challenge. Antibodies to bacterial lectins involved in attachment may be efficient inhibitors, and fimbrial vaccines have been developed. Glycosylation inhibitors have been shown to be safe and efficient in patients with lipid storage disease and might therefore be tested in urinary tract infection. This approach differs from current therapies, including antibiotics, in that it targets the pathogens which recognize these receptors.

Conditional LoxP-flanked glucosylceramide synthase allele controlling glycosphingolipid synthesis

Glycosphingolipids are organizational building blocks of plasma membranes that participate in key cellular functions, such as signaling and cell-to-cell interactions. Glucosylceramide synthase--encoded by the Ugcg gene--controls the first committed step in the major pathway of glycosphingolipid synthesis. Global disruption of the Ugcg gene in mice is lethal during gastrulation. We have now established a Ugcg allele flanked by loxP sites (floxed). When cre recombinase was expressed in the nervous system under control of the nestin promoter, the floxed gene underwent recombination, resulting in a substantial reduction of Ugcg expression and of glycosphingolipid ganglio-series levels. The mice deficient in Ugcg expression in the nervous system show a striking loss of Purkinje cells and abnormal neurologic behavior. The floxed Ugcg allele will facilitate analysis of the function of glycosphingolipids in development, physiology, and in diseases such as diabetes and cancer.

Miglustat: Substrate reduction therapy for glycosphingolipid lysisomal storage disorders

Substrate reduction therapy offers a novel approach to the treatment of lysosomal storage disorders. By reducing the rate of macromolecule synthesis to a level where the residual degradative activity in the cell is sufficient to prevent substrate accumulation, it should be possible to reverse storage and storage-related pathologies. Miglustat is an N-alkylated imino sugar that acts against a number of enzymes involved in processing glycoconjugates, including the ceramide-specific glucosyltransferase, which catalyzes the initial committed step in glycosphingolipid synthesis. Miglustat could therefore be used for substrate reduction therapy in glycosphingolipid lysosomal storage disorders. This article addresses both the preclinical and clinical development of miglustat for treatment of type 1 Gaucher's disease, as well as related neuronopathic glycosphingolipidoses.

The association of Shiga-like toxin with detergent-resistant membranes is modulated by glucosylceramide and is an essential requirement in the endoplasmic reticulum for a cytotoxic effect

Receptor-mediated internalization to the endoplasmic reticulum (ER) and subsequent retro-translocation to the cytosol are essential sequential processes required for the productive intoxication of susceptible mammalian cells by Shiga-like toxin-1 (SLTx). Recently, it has been proposed that the observed association of certain ER-directed toxins and viruses with detergent-resistant membranes (DRM) may provide a general mechanism for their retrograde transport to endoplasmic reticulum (ER). Here, we show that DRM recruitment of SLTx bound to its globotriosylceramide (Gb(3)) receptor is mediated by the availability of other glycosphingolipids. Reduction in glucosylceramide (GlcCer) levels led to complete protection against SLTx and a reduced cell surface association of bound toxin with DRM. This reduction still allowed efficient binding and transport of the toxin to the ER. However, toxin sequestration within DRM of the ER was abolished under reduced GlcCer conditions, suggesting that an association of toxin with lipid microdomains or rafts in the ER (where these are defined by detergent insolubility) is essential for a later step leading to or involving retro-translocation of SLTx across the ER membrane. In support of this, we show that a number of ER residents, proteins intimately involved in the process of ER dislocation of misfolded proteins, are present in DRM.

Establishment of cells exhibiting mutated glycolipid synthesis from mouse thymus by immortalization with SV-40 virus

Immortalization with simian virus-40 and cloning of immortalized cells from mouse thymus were performed to establish cell lines for characterization of the mode of glycolipid expression in the thymic cells. Among the 25 cell lines obtained, three lines with different morphologies were established, that is, epithelial (IMTH-E), fibroblastic (IMTH-F), and asterisk-like (IMTH-I) cells, and their glycolipids, together with those in the thymus, were determined systematically. The major glycolipids in mouse thymus were the globo- and ganglio-series, both of which, were co-expressed in the three cell lines established. However, the mode of modification of the globo- and ganglio-series was distinct for each cell line. As to the globo-series, the structures with the longest carbohydrate chain for IMTH-E, -F, and -I cells were Gb3Cer, Gb4Cer, and Forssman antigen, respectively, having stepwise shorter carbohydrates at the nonreducing termini. Although the acidic glycolipids in IMTH-E cells comprised GM3 and GM2, and their sulfated isomers, IMTH-F and -I cells expressed GMlb and GDlc for the alpha-pathway, and up to GDI a for the a-pathway of ganglio-series glycolipids. GMlb-GalNAc present in the thymus was not detected in IMTH-F and -I cells, probably due to the lower synthetic activity for the metabolic intermediate Gg4Cer. The results indicate that the immortalization technique is useful for obtaining individual cells having unique glycolipid profiles for analysis of the functional significance and metabolism of glycolipids in the thymus.

Apoptosis of human carcinoma cells in the presence of inhibitors of glycosphingolipid biosynthesis: I. Treatment of Colo-205 and SKBR3 cells with isomers of PDMP and PPMP

Apoptosis, or programmed cell death, plays an important role in many physiological and diseased conditions. Induction of apoptosis in cancer cells by anti-cancer drugs and biosynthetic inhibitors of cells surface glycolipids in the human colon carcinoma cells (Colo-205) are of interest in recent years. In our present studies, we have employed different stereoisomers of PPMP and PDMP (inhibit GlcT-glycosyltransferase (GlcT-GLT)) to initiate apoptosis in Colo-205 cells grown in culture in the presence of (3)H-TdR and (3)H/or (14)C-L-Serine. Our analysis showed that the above reagents (between 1 to 20 microM) initiated apoptosis with induction of Caspase-3 activities and phenotypic morphological changes in a dose-dependent manner. We have observed an increase of radioactive ceramide formation in the presence of a low concentration (1-4 microM) of these reagents in these cell lines. However, high concentrations (4-20 microM) inhibited incorporation of radioactive serine in the higher glycolipids. Colo-205 cells were treated with L-threo-PPMP (0-20 microM) and activities of different GSL: GLTs were estimated in total Golgi-pellets. The cells contained high activity of GalT-4 (UDP-Gal: LcOse3Cer beta 1-4galactosyltransferase), whereas negligible activity of GalT-3 (UDP-Gal: GM2 beta 1-3galactosyltransferase) or GM2-synthase activity of the ganglioside pathway was detected. Previously, GLTs involved in the biosynthetic pathway of SA-Le(x) formation had been detected in these colon carcinoma (or Colo-205) cells (Basu M et al. Glycobiology 1, 527-35 (1991)). However, during progression of apoptosis in Colo-205 cells with increasing concentrations of L-PPMP, the GalT-4 activity was decreased significantly. These changes in the specific activity of GalT-4 in the total Golgi-membranes could be the resultant of decreased gene expression of the enzyme.

New positive regulators of lin-12 activity in Caenorhabditis elegans include the BRE-5/Brainiac glycosphingolipid biosynthesis enzyme

Screens for suppressors of lin-12 hypermorphic alleles in C. elegans have identified core components and modulators of the LIN-12/Notch signaling pathway. Here we describe the recovery of alleles of six new genes from a screen for suppressors of the egg-laying defect associated with elevated lin-12 activity. The molecular identification of one of the new suppressor genes revealed it as bre-5, which had previously been identified in screens for mutations that confer resistance to Bt toxin in C. elegans. bre-5 is the homolog of D. melanogaster brainiac. BRE-5/Brainiac catalyzes a step in the synthesis of glycosphingolipids, components of lipid rafts that are thought to act as platforms for association among certain kinds of membrane-bound proteins. Reducing the activity of several other genes involved in glycosphingolipid biosynthesis also suppresses the effects of constitutive lin-12 activity. Genetic analysis and cell ablation experiments suggest that bre-5 functions prior to ligand-induced ectodomain shedding that activates LIN-12 for signal transduction.

Cell-specific deletion of glucosylceramide synthase in brain leads to severe neural defects after birth

Sialic acid-containing glycosphingolipids, i.e., gangliosides, constitute a major component of neuronal cells and are thought to be essential for brain function. UDP-glucose:ceramide glucosyltransferase (Ugcg) catalyzes the initial step of glycosphingolipid (GSL) biosynthesis. To gain insight into the role of GSLs in brain development and function, a cell-specific disruption of Ugcg was performed as indicated by the absence of virtually all glucosylceramide-based GSLs. Shortly after birth, mice showed dysfunction of cerebellum and peripheral nerves, associated with structural defects. Axon branching of Purkinje cells was significantly reduced. In primary cultures of neurons, dendritic complexity was clearly diminished, and pruning occurred early. Myelin sheaths of peripheral nerves were broadened and focally severely disorganized. GSL deficiency also led to a down-regulation of gene expression sets involved in brain development and homeostasis. Mice died approximately 3 weeks after birth. These results imply that GSLs are essential for brain maturation.

Novel class of glycosphingolipids involved in male fertility

Mice require testicular glycosphingolipids (GSLs) for proper spermatogenesis. Mutant mice strains deficient in specific genes encoding biosynthetic enzymes of the GSL pathway including Galgt1 (encoding GM2 synthase) and Siat9 (encoding GM3 synthase) have been established lacking various overlapping subsets of GSLs. Although male Galgt1-/- mice are infertile, male Siat9-/- mice are fertile. Interestingly, GSLs thought to be essential for male spermatogenesis are not synthesized in either of these mice strains. Hence, these GSLs cannot account for the different phenotypes. A novel class of GSLs was observed composed of eight fucosylated molecules present in fertile but not in infertile mutant mice. These GSLs contain polyunsaturated very long chain fatty acid residues in their ceramide moieties. GSLs of this class are expressed differentially in testicular germ cells. More importantly, the neutral subset of this new GSL class strictly correlates with male fertility. These data implicate polyunsaturated, fucosylated GSLs as essential for spermatogenesis and male mouse fertility.

Imino sugar inhibitors for treating the lysosomal glycosphingolipidoses

The inherited metabolic disorders of glycosphingolipid (GSL) metabolism are a relatively rare group of diseases that have diverse and often neurodegenerative phenotypes. Typically, a deficiency in catabolic enzyme activity leads to lysosomal storage of GSL substrates and in many diseases, several other glycoconjugates. A novel generic approach to treating these diseases has been termed substrate reduction therapy (SRT), and the discovery and development of N-alkylated imino sugars as effective and approved drugs is discussed. An understanding of the molecular mechanism for the inhibition of the key enzyme in GSL biosynthesis, ceramide glucosyltransferase (CGT) by N-alkylated imino sugars, has also lead to compound design for improvements to inhibitory potency, bioavailability, enzyme selectivity, and biological safety. Following a successful clinical evaluation of one compound, N-butyl-deoxynojirimycin [(NB-DNJ), miglustat, Zavesca], for treating type I Gaucher disease, issues regarding the significance of side effects and CNS access have been addressed as exposure of drug to patients has increased. An alternative experimental approach to treat specific glycosphingolipid (GSL) lysosomal storage diseases is to use imino sugars as molecular chaperons that assist protein folding and stability of mutant enzymes. The principles of chaperon-mediated therapy (CMT) are described, and the potential efficacy and preclinical status of imino sugars is compared with substrate reduction therapy (SRT). The increasing use of imino sugars for clinical evaluation of a group of storage diseases that are complex and often intractable disorders to treat has considerable benefit. This is particularly so given the ability of small molecules to be orally available, penetrate the central nervous system (CNS), and have well-characterized biological and pharmacological properties.

Searching new targets for anthelminthic strategies: Interference with glycosphingolipid biosynthesis and phosphorylcholine metabolism affects development of Caenorhabditis elegans

Nematode infections are amongst the most abundant diseases of man and animals. They are characterised by a low mortality but high morbidity, thus reflecting the adaptation of these parasites to their hosts. Resistance as well as severe side-effects and efficacies restricted to distinct larval stages or parasites of the anthelmithics used at present require the urgent development of new and more nematode-specific drugs, targeting enzymes of parasite restricted biosynthetic routes. Caenorhabditis elegans has been found to be a good model system for parasitic nematodes, drug screening and developmental studies. Structural analyses have revealed nematode-specific glycosphingolipid structures of the arthro-series, carrying in part, phosphorylcholine substituents. These biomolecules appear to play important roles in nematode development, fertility and survival within the host and are, therefore, good target-candidates for the development of new anthelminthic strategies. Here we show that RNAi experiments targeting enzymes of glycosphingolipid biosynthesis or choline metabolism result, in part, in a drastic reduction of fertility. We further tested various chemical inhibitors of these pathways and found significant effects on the development of the worms, resulting in developmental arrest, sterility and, in part, lethality. Such inhibitors can, therefore, help to define new classes of anthelminthics.

SKN1, a novel plant defensin-sensitivity gene inSaccharomyces cerevisiae, is implicated in sphingolipid biosynthesis

The antifungal plant defensin DmAMP1 interacts with the fungal sphingolipid mannosyl diinositolphosphoryl ceramide (M(IP)(2)C) and induces fungal growth inhibition. We have identified SKN1, besides the M(IP)(2)C-biosynthesis gene IPT1, as a novel DmAMP1-sensitivity gene in Saccharomyces cerevisiae. SKN1 was previously shown to be a KRE6 homologue, which is involved in beta-1,6-glucan biosynthesis. We demonstrate that a Deltaskn1 mutant lacks M(IP)(2)C. Interestingly, overexpression of either IPT1 or SKN1 complemented the skn1 mutation, conferred sensitivity to DmAMP1, and resulted in M(IP)(2)C levels comparable to the wild type. These results show that SKN1, together with IPT1, is involved in sphingolipid biosynthesis in S. cerevisiae.

Comparative characteristics of three human embryonic stem cell lines

Human embryonic stem (hES) cells have unique features including unlimited growth capacity, expression of specific markers, normal karyotypes and an ability to differentiate. Many investigators have tried to use hES cells for cell-based therapy, but there is little information about the properties of available hES cell lines. We compared the characteristics of three hES cell lines. The expression of SSEA-1, -3, -4, and APase, was examined by immunocytochemistry, and Oct-4 expression was analyzed by RT-PCR. Differentiation of the hES cells in vitro and in vivo led to the formation of embryoid bodies (EBs) or teratomas. We examined the expression of tissue-specific markers in the differentiated cells by semiquantitative RT-PCR, and the ability of each hES cell line to proliferate was measured by flow cytometry of DNA content and ELISA. The three hES cell lines were similar in morphology, marker expression, and teratoma formation. However there were significant differences (P < 0.05) between the differentiated cells formed by the different cell lines in levels of expression of tissue-specific markers such as renin, kallikrein, Glut-2, beta- and delta-globin, albumin, and alpha1-antitrypsin (alpha1-AT). The hES cell lines also differed in proliferative activity. Our observations should be useful in basic and clinical hES cell research.

The pathogenesis of glycosphingolipid storage disorders

Glycosphingolipid storage disorders are inborn errors of metabolism caused by the defective activity of degradative enzymes in lysosomes. In this review, we summarize studies performed over the past few years attempting to define the secondary and down-stream biochemical and cellular pathways affected in GSL storage disorders that are responsible for neuronal dysfunction, a characteristic of most of these disorders. We focus mainly on the regulation of intracellular calcium homeostasis and phospholipid biosynthesis. These studies may help unravel new roles for glycosphingolipids in the regulation of normal cell physiology, as well as suggest potential new therapeutic options in the glycosphingolipid and other lysosomal storage disorders.

A critical role for lipophosphoglycan in proinflammatory responses of dendritic cells toLeishmania mexicana

Recognition of pathogen-associated molecular patterns (PAMP) influences the response of dendritic cells (DC) and therefore development of innate and adaptive immunity. Different forms of Leishmania mexicana have distinct effects on DC, with promastigotes and amastigotes being activating and apparently neutral, respectively. We investigated whether stage-specific differences in surface composition might account for these distinct effects. Amastigotes and promastigotes lacking the lpg1 gene needed for lipophosphoglycan (LPG) biosynthesis could not activate DC in vitro. Genome-wide transcriptional profiling of DC infected with wild-type or mutant promastigotes or wild-type amastigotes revealed that wild-type promastigotes induce an inflammatory signature that is lacking in DC exposed to the other parasite forms. The proinflammatory response pattern was partly recovered by reconstitution of lpg1 expression in lpg1-/- parasites, and exposure to purified LPG increased the expression of MHC class II and CD86 on DC. Infection with wild-type but not lpg1-/- promastigotes increased the number of activated DC in draining lymph nodes, and this was correlated with lower early parasite burdens in wild-type-infected animals. These in vivo and in vitro results suggest an LPG-dependent activation of DC that contributes to host defense and agree with the notion that the parasites evolved under immune pressure to down-regulate PAMP expression in mammalian hosts.

Leishmania braziliensis: a novel mechanism in the lipophosphoglycan regulation during metacyclogenesis

During metacyclogenesis of Leishmania in its sand fly vector, the parasite differentiates from a noninfective, procyclic form to an infective, metacyclic form, a process characterised by morphological changes of the parasite and also biochemical transformations in its major surface lipophosphoglycan (LPG). This lipid-anchored polysaccharide is polymorphic among species with variations in sugars that branch off the conserved Gal(beta1,4)Man(alpha1)-PO4 backbone of repeat units and the oligosaccharide cap. Lipophosphoglycan has been implicated as an adhesion molecule that mediates the interaction with the midgut epithelium of the sand fly in the subgenus Leishmania. This paper describes the LPG structure for the first time in a species from the subgenus Viannia, Leishmania (Viannia) braziliensis. The LPG from the procyclic form of L. braziliensis was found to lack side chain sugar substitutions. In contrast to other species from the subgenus Leishmania, metacyclic forms of L. braziliensis makes less LPG and add 1-2 (beta1-3) glucose residues that branch off the disaccharide-phosphate repeat units of LPG. Thus, this represents a novel mechanism in the regulation of LPG structure during metacyclogenesis.