Chemistry and functional distribution of sulfoglycolipids

Unique disialosyl gangliosides from salmon kidney: Characterization of V3αFuc, IV3βGalNAc, II3(αNeuAc)2-Gg4Cer and its analogue with 4-O-acetyl-N-acetylneuraminic acid

Four unidentified acidic glycolipids (X3-X6) were isolated from the kidney of the Pacific salmon on an anion exchange column and by high performance liquid chromatography using a silica bead (Iatrobeads) column. Based on methylation analysis, chemical and enzymatic degradation, proton nuclear magnetic resonance spectroscopy and mass spectrometry, the glycon structure of X5 and X6 was identified as a unique disialosyl fucosyl-N-acetylgalactosaminyl ganglio-N-tetraose:Fucalpha3GalNAcbeta3Galbeta3GalNAcbeta4[NeuAcalpha8NeuAcalpha3] Galbeta4Glcbeta1Cer. NMR showed that X3 and X4 were analogues of X5 and X6 and contained O-acetyl groups on C4 of the outer N-acetylneuraminic acid, first disialosyl gangliosides containing 4-O-acetyl-N-acetylneuraminic acid. The ceramides of X3 and X5 contained predominantly C24: 1, and X4 and X6 contained saturated fatty acids (C14: 0, C16: 0 and C18: 0), whereas the long chain base was exclusively sphingenine. The concentrations of X3 and X4 were 0.13 and 0.16 nmol/g of kidney respectively and those of X5 and X6, were 0.07 nmol/g each.

Regulatory effect of sulphatides on BKCa channels

BACKGROUND AND PURPOSE

Sulphatides are sulphated glycosphingolipids expressed on the surface of many cell types, particularly neurones. Changes in sulphatide species or content have been associated with epilepsy and Alzheimer's disease. As the large conductance, calcium sensitive K(+) channel (BK(Ca)) are modulated by membrane lipids, the aim of the study was to explore possible effects of sulphatides on BK(Ca) channels.

EXPERIMENTAL APPROACH

Using patch-clamp techniques, we studied effects of exogenous sulphatides on BK(Ca) channels expressed in Chinese hamster ovary cells.

KEY RESULTS

Sulphatides reversibly increased the whole-cell current and the single channel open probability of BK(Ca) channels dose-dependently. The EC(50) value on the channel at +10 mV was 1.6 microM and the Hill coefficient was 2.5. In inside-out patches, sulphatides increased the single channel open probability from both intra- and extra-cellular faces of the membrane, but more effectively with external application. Furthermore, activation of the channels by sulphatides was independent of intracellular Ca(2+) concentration. Sulphatides also shifted the activation curve of the channels to less positive membrane potentials. Mutant BK(Ca) channels lacking a 59 aminoacid region important for amphipath activation (STREX) were less activated by the sulphatides.

CONCLUSIONS AND IMPLICATIONS

Sulphatides are novel activators of BK(Ca) channels, independent of intracellular Ca(2+) or other signalling molecules but partly dependent on the STREX sequence of the channel protein. As changes of sulphatide content are associated with neuronal dysfunction, as in epilepsy and Alzheimer's disease, our results imply that these effects of sulphatides may play important pathophysiological roles in regulation of BK(Ca) channels.

Uptake of the glycosphingolipid sulfatide in the gastrointestinal tract and pancreas in vivo and in isolated islets of Langerhans

Background

The glycosphingolipid sulfatide has previously been found in several mammalian tissues, but information on the uptake of exogenously administered sulfatide in different organs in vivo is limited. In pancreatic beta cells, sulfatide has been shown to be involved in insulin processing and secretion in vitro. In this study, we examined the uptake of exogenously administered sulfatide and its distribution to the pancreatic beta cells. This might encourage future studies of the function(s) of sulfatide in beta cell physiology in vivo. Radioactive sulfatide was given orally to mice whereafter the uptake of sulfatide in the gastrointestinal tract and subsequent delivery to the pancreas was examined. Sulfatide uptake in pancreas was also studied in vivo by i.p. administration of radioactive sulfatide in mice, and in vitro in isolated rat islets. Isolated tissue/islets were analysed by scintillation counting, autoradiography and thin-layer chromatography-ELISA.

Results

Sulfatide was taken up in the gastrointestinal tract for degradation or further transport to other organs. A selective uptake of short chain and/or hydroxylated sulfatide fatty acid isoforms was observed in the small intestine. Exogenously administered sulfatide was found in pancreas after i.p, but not after oral administration. The in vitro studies in isolated rat islets support that sulfatide, independently of its fatty acid length, is endocytosed and metabolised by pancreatic islets.

Conclusion

Our study supports a selective uptake and/or preservation of sulfatide in the gastrointestinal tract after oral administration and with emphasises on pancreatic sulfatide uptake, i.p. administration results in sulfatide at relevant location.

P-selectin mediates metastatic progression through binding to sulfatides on tumor cells

Hematogenous carcinoma metastasis is associated with tumor cell emboli formation, which is now known to be facilitated by selectins. P-selectin-mediated interactions of platelets with cancer cells are based mostly on mucin- and glycosaminoglycan-type selectin ligands. We previously showed that mouse colon carcinoma cells (MC-38) carry P-selectin ligands of nonmucin origin, which were not identified. Here we show that P-selectin ligands recognized on MC-38 cells are sulfated glycolipids, thereby facilitating experimental metastasis in a syngeneic mouse model. Metabolic inhibition of sulfation by incubation of cells with sodium chlorate almost completely abrogated P-selectin binding. Metabolic labeling of MC-38 cells with (35)S sulfate revealed only a single band as detected by high-performance thin layer chromatography analysis of a total lipid extract. Matrix-assisted laser desorption/ionization tandem time-of-flight/time-of-flight analysis (MALDI-TOF-TOF) analysis of the purified sulfate-containing lipid fraction identified the selectin ligand to be a sulfated galactosylceramide SM4 (HSO(3)-3Galbeta-1Cer). Modulation of glycolipid biosynthesis in MC-38 cells altered P-selectin binding, thereby confirming sulfoglycolipids to be major P-selectin ligands. In addition, P-selectin was also found to recognize lactosylceramide sulfate SM3 (HSO(3)-3Galbeta-4Glcbeta-1Cer) and gangliotriaosylceramide sulfate SM2 [GalNAcbeta-4(HSO(3)-3)Galbeta-4Glcbeta-1Cer] in human hepatoma cells. Finally, the enzymatic removal of sulfation from the cell surface of MC-38 cells resulted in decreased P-selectin binding and led to attenuation of metastasis. Thus, SM4 sulfatide serves as a native ligand for P-selectin contributing to cell-cell interactions and to facilitation of metastasis.

Embryonic stem cell-based reduction of central nervous system sulfatide storage in an animal model of metachromatic leukodystrophy

Pluripotency, virtually unlimited self-renewal and amenability to genetic modification make embryonic stem (ES) cells an attractive donor source for cell-mediated gene therapy. In this proof of concept study, we explore whether glial precursors derived from murine ES cells (ESGPs) and engineered to overexpress human arylsulfatase A (hASA) can cross-correct the metabolic defect in an animal model of metachromatic leukodystrophy (MLD). Transfected ES cells showed an up to 30-fold increase in ASA activity. Following in vitro differentiation, high expression of ASA was found in all stages of neural and glial differentiation. hASA-overexpressing ESGPs maintained their ability to differentiate into astrocytes and oligodendrocytes in vitro and in vivo. After transplantation into the brain of neonatal ASA-deficient mice, hASA-overexpressing ESGPs were found to incorporate into a variety of host brain regions. Four weeks after engraftment, immunofluorescence analyses with an antibody to sulfatide revealed a 46.7+/-4.0% reduction of immunoreactive sulfatide deposits in the vicinity of the hASA-positive engrafted cells, thereby significantly extending the rate of sulfatide reduction achieved by the endogenous ASA activity of non-hASA-transfected control cells (21.1+/-5.8%). These findings provide first in vivo evidence that ES cells may serve as a potential donor source for cell-mediated enzyme delivery in storage disorders such as MLD.

Sulfatide with short fatty acid dominates in astrocytes and neurons

Glycosphingolipids are located in cell membranes and the brain is especially enriched. We speculated that the subcellular location of glycosphingolipids depends on their fatty acid chain length because their sugar residues are constant, whereas fatty acid chain length can vary within the same molecule. To test this hypothesis we analysed the glycosphingolipid sulfatide, which is highly abundant in myelin and has mostly long fatty acids. We used a negative ion electrospray tandem mass spectrometry precursor ion scan to analyse the molecular species of sulfatide in cultured astrocytes and a mouse model of the human disease metachromatic leukodystrophy. In these arylsulfatase A (ASA)-deficient mice sulfatide accumulates intracellularly in neurons and astrocytes. Immunocytochemistry was also performed on cultured astrocytes and analysed using confocal laser scanning microscopy. Analyses of the molecular species showed that cultured astrocytes contained sulfatide with a predominance of stearic acid (C18), which was located in large intracellular vesicles throughout the cell body and along the processes. The same was seen in ASA-deficient mice, which accumulated a higher proportion (15 mol% compared with 8 mol% in control mice) of sulfatide with stearic acid. We conclude that the major fatty acid composition of sulfatide differs between white and grey matter, with neurons and astrocytes containing mostly short-chain fatty acids with an emphasis on stearic acid. Based on our results, we speculate that the fatty acid chain length of sulfatide might determine its intracellular (short chain) or extracellular (long chain) location and thereby its functions.

The crystal structure of SdsA1, an alkylsulfatase from Pseudomonas aeruginosa, defines a third class of sulfatases

Pseudomonas aeruginosa is both a ubiquitous environmental bacterium and an opportunistic human pathogen. A remarkable metabolic versatility allows it to occupy a multitude of ecological niches, including wastewater treatment plants and such hostile environments as the human respiratory tract. P. aeruginosa is able to degrade and metabolize biocidic SDS, the detergent of most commercial personal hygiene products. We identify SdsA1 of P. aeruginosa as a secreted SDS hydrolase that allows the bacterium to use primary sulfates such as SDS as a sole carbon or sulfur source. Homologues of SdsA1 are found in many pathogenic and some nonpathogenic bacteria. The crystal structure of SdsA1 reveals three distinct domains. The N-terminal catalytic domain with a binuclear Zn2+ cluster is a distinct member of the metallo-beta-lactamase fold family, the central dimerization domain ensures resistance to high concentrations of SDS, whereas the C-terminal domain provides a hydrophobic groove, presumably to recruit long aliphatic substrates. Crystal structures of apo-SdsA1 and complexes with substrate analog and products indicate an enzymatic mechanism involving a water molecule indirectly activated by the Zn2+ cluster. The enzyme SdsA1 thus represents a previously undescribed class of sulfatases that allows P. aeruginosa to survive and thrive under otherwise bacteriocidal conditions.

Rapid demonstration of diversity of sulfatide molecular species from biological materials by MALDI-TOF MS

By combining the partition method for enrichment of sulfatides without any chromatographic procedures and the preparation method of lysosulfatides, we succeeded in analyzing these sulfated glycosphingolipids from biological materials by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) to reduce the complexity of mass fragmentation patterns within a day. We found that sulfated GalCer (HSO3-3Gal beta 1Cer) (SM4s [galactosylsulfatide]) was composed of different species. While composition of SM4s specifically depended on source materials, it always contained hydroxy fatty acids of various degrees. In addition to the common sphingoid 4-sphingenine (d18:1), uncommon/unusual sphingoids phytosphingosine (4-hydroxysphinganine) (t18:0), eicosasphinganine (d20:0), 4-eicosasphingenine (d20:1), and sphingadienine (d18:2) were easily detected. Finally, in addition to SM4s, sulfatide sulfated LacCer (HSO3-3Gal beta 4Glc beta 1Cer) (SM3 [sulfated lactosylceramide]) and sulfated Gg3Cer (GalNAc beta 4(HSO3-3)Gal beta 4Glc beta 1Cer) (SM2 [sulfated gangliotriaosylceramide]) were clearly detected in renal tubule cells. The major SM4s was composed of ceramides possessing d18:1 with C22 hydroxy fatty acids (C22:0 h), C23:0 h, and C24:0 h, whereas the major SM3/SM2 were composed of ceramides possessing t18:0 with C22 normal fatty acids (C22:0), C23:0, C24:0. Namely, in these two series of sulfatides, either fatty acids or sphingoids were hydroxylated, and chain lengths of these components were exactly the same, consequently resulting in a similar polarity of ceramide moieties in these sulfatide species. These results demonstrated diversities of sulfatide molecular species, not only with respect to sugar moieties but also to ceramide moieties, which are probably important for specific effective functions in particular microenvironments such as lipid membrane microdomains.

Isolation and identification of nine sulfated glycosphingolipids containing two unique sulfated gangliosides from the African green monkey kidney cells, Verots S3, and their possible metabolic pathways

Verots S3 cells derived from the African green monkey kidney were revealed to contain nine types of sulfoglycolipids by incorporating [35S]sulfate. These sulfated glycolipids were separated by DEAE-Sephadex column chromatography and preparative thin-layer chromatography (TLC). The major sulfoglycolipids were characterized using TLC, gas-liquid chromatography (GLC), mass spectrometry, solvolysis, TLC immunostaining, and nuclear magnetic resonance spectra as follows: V1, SM4s (GalCer I3-sulfate); V2, SM3 (LacCer II3-sulfate); V3, SM2a (Gg3Cer II3-sulfate); V4, globopentaosyl ceramide sulfate (Gb5Cer V3-sulfate); V5, (Gg4Cer II3-sulfate, IV3-NeuAc); V6, SB1a (Gg4Cer II3, IV3-bis-sulfate); and V8, (Gg4Cer II3-NeuAc, IV3-sulfate). Both V5 and V8 were sulfated gangliosides comprising both N-acetyl neuraminic acid and sulfate, and this was the first report on V8. A minor component V7 was identified as SM1a (Gg4Cer II3-sulfate) based on its behavior in TLC, GLC, and liquid secondary ion mass spectroscopy. It was postulated that this substance was a precursor of V6 (SB1a) and V5 (Gg4Cer II3-sulfate, IV3-NeuAc), and to date, its presence has not been demonstrated in nature. Another minor component V9 was identified as glucosyl ceramide sulfate based on its migration in TLC and GLC. This renal cell line was shown to be an excellent model for studying the metabolism and function of sulfoglycolipids.

Glycosphingolipid-facilitated membrane insertion and internalization of cobra cardiotoxin. The sulfatide.cardiotoxin complex structure in a membrane-like environment suggests a lipid-dependent cell-penetrating mechanism for membrane binding polypeptides

Cobra cardiotoxins, a family of basic polypeptides having lipid- and heparin-binding capacities similar to the cell-penetrating peptides, induce severe tissue necrosis and systolic heart arrest in snakebite victims. Whereas cardiotoxins are specifically retained on the cell surface via heparan sulfate-mediated processes, their lipid binding ability appears to be responsible, at least in part, for cardiotoxin-induced membrane leakage and cell death. Although the exact role of lipids involved in toxin-mediated cytotoxicity remains largely unknown, monoclonal anti-sulfatide antibody O4 has recently been shown to inhibit the action of CTX A3, the major cardiotoxin from Taiwan cobra venom, on cardiomyocytes by preventing cardiotoxin-induced membrane leakage and CTX A3 internalization into mitochondria. Here, we show that anti-sulfatide acts by blocking the binding of CTX A3 to the sulfatides in the plasma membrane to prevent sulfatide-dependent CTX A3 membrane pore formation and internalization. We also describe the crystal structure of a CTX A3-sulfatide complex in a membrane-like environment at 2.3 angstroms resolution. The unexpected orientation of the sulfatide fatty chains in the structure allows prediction of the mode of toxin insertion into the plasma membrane. CTX A3 recognizes both the headgroup and the ceramide interfacial region of sulfatide to induce a lipid conformational change that may play a key role in CTX A3 oligomerization and cellular internalization. This proposed lipid-mediated toxin translocation mechanism may also shed light on the cellular uptake mechanism of the amphiphilic cell-penetrating peptides known to involve multiple internalization pathways.

Cobra cardiotoxin-induced cell death in fetal rat cardiomyocytes and cortical neurons: different pathway but similar cell surface target

Cobra cardiotoxins (CTXs) are basic polypeptides with diverse pharmacological functions that are cytotoxic to many different cell types through both necrotic and apoptotic cell death pathways. In this comparative study of the action of CTX A3 from the Taiwan cobra (Naja atra) on fetal rat cardiomyocytes and cortical neurons, it was shown that CTX A3 induced different patterns of elevation of intracellular Ca2+ concentration ([Ca2+]i), CTX internalization, caspase-3 activity and viability. Application of an anti-sulfatide monoclonal antibody, O4 specific for 3-sulfo-galactose lipid, but not in the control experiments using anti-GM3 monoclonal antibody, reduces CTX-induced [Ca2+]i elevation, CTX internalization and toxicity. Therefore, CTX may target similar sulfo-containing cell surface receptors in both fetal rat cardiomyocytes and cortical neurons, but induce cell death through different pathways specific to each cell type.

Laminin-sulfatide binding initiates basement membrane assembly and enables receptor signaling in Schwann cells and fibroblasts

Endoneurial laminins (Lms), β1-integrins, and dystroglycan (DG) are important for Schwann cell (SC) ensheathment and myelination of axons. We now show that SC expression of galactosyl-sulfatide, a Lm-binding glycolipid, precedes that of Lms in developing nerves. This glycolipid anchors Lm-1 and -2 to SC surfaces by binding to their LG domains and enables basement membrane (BM) assembly. Revealingly, non–BM-forming fibroblasts become competent for BM assembly when sulfatides are intercalated into their cell surfaces. Assembly is characterized by coalescence of sulfatide, DG, and c-Src into a Lm-associated complex; by DG-dependent recruitment of utrophin and Src activation; and by integrin-dependent focal adhesion kinase phosphorylation. Collectively, our findings suggest that sulfated glycolipids are key Lm anchors that determine which cell surfaces can assemble Lms to initiate BM assembly and DG- and integrin-mediated signaling.

CD1a and CD1c activate intrathyroidal T cells during Graves' disease and Hashimoto's thyroiditis

Molecular studies have shown that CD1 proteins present self and foreign lipid Ags to T cells, but the possible roles of CD1 in human autoimmune diseases in vivo are not known, especially for the group 1 CD1 isoforms (CD1a, CD1b, and CD1c). To investigate the hypothesis that CD1-restricted T cells might be activated and home to target tissues involved in Hashimoto's thyroiditis and Graves' disease, we performed ex vivo analysis of lymphocytes from peripheral blood and autoinflammatory lesions of thyroid tissue. Immunofluorescence analysis identified two types of CD1-expressing APCs in inflamed thyroid tissues. CD1a, CD1b, and CD1c were expressed on CD83+ dendritic cells, and CD1c was expressed on an abundant population of CD20+ IgD+ CD23- CD38- B cells that selectively localized to the mantle zone of lymphoid follicles within the thyroid gland. CD1c-restricted, glycolipid-specific T cells could not be detected in the peripheral blood, but were present in polyclonal lymphocyte populations isolated from affected thyroid glands. In addition, polyclonal thyroid-derived lymphocytes and short-term T cell lines were found to recognize and lyse targets in a CD1a- or CD1c-dependent manner. The targeting of CD1-restricted T cells and large numbers of CD1-expressing APCs to the thyroid gland during the early stages of autoimmune thyroiditis suggests a possible effector function of CD1-restricted T cells in tissue destruction and point to a new model of organ-specific autoimmune disease involving lipid Ag presentation.

Chemokines bind to sulfatides as revealed by surface plasmon resonance

Chemokines bind to sulfated cell surface glycosaminoglycans and thereby modulate signaling mediated by G-protein-coupled seven-transmembrane domain chemokine receptors. Similar to glycosaminoglycans, sulfated oligosaccharides are also exposed on the cell surface by sulfatides, a class of glycosphingolipids. We have now identified sulfated glycosphingolipids (sulfatides) as novel binding partners for chemokines. Using surface plasmon resonance (SPR), the binding of proinflammatory and homeostatic chemokines to glycosphingolipids, in particular sulfatides, was investigated. Chemokines were immobilized while glycosphingolipids or additional phospholipids incorporated into liposomes were applied as soluble analytes. A specific affinity of the chemokines MCP-1/CCL2, IL-8/CXCL8, SDF-1alpha/CXCL12, MIP-1alpha/CCL3 and MIP-1beta/CCL4 to the sulfatides SM4s, SM3, SM2a and SB2, SB1a was detected. No significant interactions with the chemokines were observed for gangliosides, neutral glycosphingolipids or phospholipids. Chemokine receptors have been associated with the detergent-insoluble fraction supposed to contain 'rafts', i.e., glycosphingolipid enriched microdomains of the cell surface. Accordingly, the data suggest that early chemokine receptor signaling may take place in the vicinity of sulfated glycosphingolipids on the cell surface, whereby these sulfatides could modulate the chemokine receptor-mediated cell activation signal.

Biological roles of sulfoglycolipids and pathophysiology of their deficiency

Mammalian sulfoglycolipids are comprised of two major members, sulfatide (SO(3)-3Gal-ceramide) and seminolipid (SO(3)-3Gal-alkylacylglycerol). Sulfatide is abundant in the myelin sheath and seminolipid is expressed on the spermatogenic cells. Cerebroside sulfotransferase (CST)-deficient mice generated by gene targeting completely lack sulfatide and seminolipid all over the body. CST-null mice manifest some neurological disorders due to myelin dysfunction, an aberrant enhancement of oligodendrocyte terminal differentiation, and an arrest of spermatogenesis, indicating that sulfation of glycolipids is essential for myelin formation and spermatogenesis. Moreover, CST-deficiency ameliorates L-selectin-dependent monocyte infiltration in the kidney after ureteral obstruction, an experimental model of renal interstitial inflammation, indicating that sulfatide is an endogenous ligand of L-selectin. Studies on the molecular mechanisms by which sulfoglycolipids participate in these biological processes are ongoing.

Percoll Gradient-Centrifuged Capacitated Mouse Sperm Have Increased Fertilizing Ability and Higher Contents of Sulfogalactosylglycerolipid and Docosahexaenoic Acid-Containing Phosphatidylcholine Compared to Washed Capacitated Mouse Sperm1

Although Percoll gradient centrifugation has been used routinely to prepare motile human sperm, its use in preparing motile mouse sperm has been limited. Here, we showed that Percoll gradient-centrifuged (PGC) capacitated mouse sperm had markedly higher fertilizing ability (sperm-zona pellucida [ZP] binding and in vitro fertilization) than washed capacitated mouse sperm. We also showed that the lipid profiles of PGC capacitated sperm and washed capacitated sperm differed significantly. The PGC sperm had much lower contents of cholesterol and phospholipids. This resulted in relative enrichment of male germ cell-specific sulfogalactosylglycerolipid (SGG), a ZP-binding ligand, in PGC capacitated sperm, and this would explain, in part, their increased ZP-binding ability compared with that of washed capacitated sperm. Analyses of phospholipid fatty acyl chains revealed that PGC capacitated sperm were enriched in phosphatidylcholine (PC) molecular species containing highly unsaturated fatty acids (HUFAs), with docosahexaenoic acid (DHA; C22: 6n-3) being the predominant HUFA (42% of total hydrocarbon chains of PC). In contrast, the level of PC-HUFAs comprising arachidonic acid (20:4n-6), docosapentaenoic acid (C22:5n-6), and DHA in washed capacitated sperm was only 27%. Having the highest unsaturation degree among all HUFAs in PC, DHA would enhance membrane fluidity to the uppermost. Therefore, membranes of PGC capacitated sperm would undergo fertilization-related fusion events at higher rates than washed capacitated sperm. These results suggested that PGC mouse sperm should be used in fertilization experiments and that SGG and DHA should be considered to be important biomarkers for sperm fertilizing ability.

Metabolism of sulfolipids in isolated renal tubules from rat

Proximal-rich tubules were prepared from rat kidneys by using collagenase treatment. The isolated rat renal tubules were compared with the intact kidney on the following characteristics. (1) Composition of the sulfoglycolipid. (2) Sulfoglycolipid metabolism based on incorporation of [35S]sulfate or some properties of sulfoglycolipid metabolism, including the activities of anabolic and catabolic enzymes. The results indicated following characteristics of the isolated renal tubules in comparison to the kidney in vivo. (1) The sulfoglycolipid compositions are qualitatively similar, except that the content of glucosyl sulfatide, Gg3Cer II3-sulfate, and GM4 was slightly higher in the isolated tubules. (2) The apparent half-lives (15-55 min) of sulfoglycolipids in the isolated tubules could indicate the existence of a rapid turnover pool of these lipids. (3) The sulfotransferase and sulfatase activities related to sulfoamphiphiles in the renal tubule were similar to those reported for the whole kidney. Based on the above criteria, we conclude that the isolated rat renal tubule should be a useful metabolic system for clarification of the short-term physiological events, up to 90 min, of proximal tubular sulfoglycolipids. By using the present system, we showed that biosynthesis of the renal total sulfoglycolipid was significantly elevated in rats deprived of water for 24 h.

Galectin-4 Binds to Sulfated Glycosphingolipids and Carcinoembryonic Antigen in Patches on the Cell Surface of Human Colon Adenocarcinoma Cells

Galectin-4, a member of the galectin family, is expressed in the epithelium of the alimentary tract. It has two tandemly repeated carbohydrate recognition domains and specifically binds to an SO3- -->3Galbeta1-->3GalNAc pyranoside with high affinity (Ideo, H., Seko, A., Ohkura, T., Matta, K. L., and Yamashita, K. (2002) Glycobiology 12, 199-208). In this study, we found that galectin-4 binds to glycosphingolipids carrying 3-O-sulfated Gal residues, such as SB1a, SM3, SM4s, SB2, SM2a, and GM1, but not to glycosphingolipids with 3-O-sialylated Gal, such as sLc4Cer, snLc4Cer, GM3, GM2, and GM4, using both an enzyme-linked immunosorbent assay and a surface plasmon resonance assay. A confocal immunocytochemical assay showed that galectin-4 was colocalized with SB1a, GM1, and carcinoembryonic antigen (CEA) in the patches on the cell surface of human colon adenocarcinoma CCK-81 and LS174T cells. This localization was distinct from caveolin/VIP21 localization. Furthermore, immobilized galectin-4 promoted adhesion of CCK-81 cells through the sulfated glycosphingolipid, SB1a. CEA also bound to galectin-4 with KD value of 2 x 10(-8) m by surface plasmon resonance and coimmunoprecipitated with galectin-4 in LS174T cell lysates. These findings suggest that SB1a and CEA in the patches on the cell surface of human colon adenocarcinoma cells could be biologically important ligands for galectin-4.

Testis-specific sulfoglycolipid, seminolipid, is essential for germ cell function in spermatogenesis

More than 90% of the glycolipid in mammalian testis consists of a unique sulfated glyceroglycolipid, seminolipid. The sulfation of the molecule is catalyzed by a Golgi membrane-associated sulfotransferase, cerebroside sulfotransferase (CST). Disruption of the Cst gene in mice results in male infertility due to the arrest of spermatogenesis prior to the metaphase of the first meiosis. However, the issue of which side of the cell function-germ cells or Sertoli cells-is deteriorated in this mutant mouse remains unknown. Our findings show that the defect is in the germ cell side, as evidenced by a transplantation analysis, in which wild-type spermatogonia expressing the green fluorescent protein were injected into the seminiferous tubules of CST-null testis. The transplanted GFP-positive cells generated colonies and spermatogenesis proceeded over meiosis in the mutant testis. The findings also clearly show that the seminolipid is expressed on the plasma membranes of spermatogonia, spermatocytes, spermatids, and spermatozoa, as evidenced by the immunostaining of wild-type testes using an anti-sulfogalactolipid antibody, Sulph-1 in comparison with CST-null testes as a negative control, and that seminolipid appears as early as day 8 of age, when Type B spermatogonia emerge.

Characterization of autoantibodies against sulfatide from a V-gene phage-display library derived from patients with systemic lupus erythematosus

Sulfatide, ceramide galactosyl-3'-sulfate, is mainly present in nervous tissue, kidney, testis, red blood cells, platelets and granulocyte. Antibodies to sulfatide are present in many patients with demyelinating peripheral neuropathy, HIV infection and systemic lupus erythematosus and may account for some of the clinical manifestations. To evaluate the effect of such antibodies, we have constructed a phage-display antibody fragment library from the lymphocytes of patients with systemic lupus erythematosus. Sulfatide-reactive phage were selected by absorption and elution on sulfatide liposomes and soluble single chain variable fragment (ScFv) were isolated from individual colonies and tested in an ELISA assay for binding to bovine brain sulfatide. Five ScFv clones that bound sulfatide were isolated. Two of the clones, PH5 and PA38, bound sulfatide but not phosphatidylserine, phosphatidylcholine, phosphatidylethanolamine, sphingomyelin or ceramide. These two clones also bound sulfatide from human red blood cells. The DNA encoding the fragments was sequenced, revealing predicted polypeptides of 19 kDa for PH5 containing only variable heavy (VH) sequences, and 31 kDa for PA38, with both VH and variable light (VL) sequences. Although they had similar antigen specificities, the VH domains of the two clones were derived from different heavy-chain families. The clustered mutational patterns in the complementarity-determining region (CDR) of the heavy chains in both clones suggest that the V-domains are the products of antigen-driven B cell clonal maturation leading to the development of sulfatide-binding specificity. These results show the presence of sulfatide-specific antibodies in lupus patients, and allow us to test the possibility that the interaction of the antibodies with sulfatide may contribute to some of the symptoms. In addition, the antibodies provide useful reagents to test the role of sulfatide in pathophysiological processes.

The role of sulfatide in thrombogenesis and haemostasis

In 1961, Wago et al. reported a potential anticoagulant role for sulfatide using animal experiments. Since then there have been many studies of sulfatide in the field of thrombogenesis/haemostasis, yielding contradictory conclusions. Some report that sulfatide has anti-thrombotic activity because it prolongs clotting time, inhibits platelet adhesion, and prolongs bleeding. Others report that sulfatide induces thrombosis in animal models. This mini-review is a chronologic review of reports examining the role of sulfatide in thrombogenesis/haemostasis together with the introduction of data from our laboratory and a discussion of the possible mechanisms underlying these curious phenomena.

Selective lack of the C16:0 fatty acid isoform of sulfatide in pancreas of type II diabetic animal models

Sulfatide (3'-sulfogalactosyl-ceramide) is a glycosphingolipid mainly located in the nervous system, but has also been found in the islets of Langerhans. Previous studies have suggested that sulfatide is involved in insulin processing and secretion. In this study, sulfatide expression and metabolism in pancreas and isolated islets of the type II diabetes models, ob/ob- and db/db mouse, was investigated using TLC-ELISA, metabolic labelling and electron microscopy. As in non-diabetic Lewis rat and human pancreas, sulfatide was located in secretory granules of the beta cells. However, the type II diabetic animal models and their background strains had an altered sulfatide expression, involving the lack of the C16:0 sulfatide fatty acid isoform, compared to non-diabetic Lewis rat, BALB/c mouse and human pancreatic tissue, in which the two dominating pancreatic sulfatide isoforms C16:0 and C24:0 are expressed. Correspondingly, in isolated ob/ob islets, sulfatide synthesis excluded the production of C16:0 sulfatide. Insulin administration to ob/ob mouse, which lowers beta cell activity, resulted in significantly increased sulfatide expression in pancreas (p=0.0003), but still no expression of the C16:0 sulfatide isoform. In vitro, the C16:0 sulfatide was shown to be the isomer involved in the preservation of insulin crystals. Thus, it is hypothesized that the selection of sulfatide isomers in pancreas might be a genetic factor contributing to disease development in type II diabetic animal models.

Cerebroside sulfotransferase deficiency ameliorates L-selectin-dependent monocyte infiltration in the kidney after ureteral obstruction

Mononuclear cells infiltrating the interstitium are involved in renal tubulointerstitial injury. The unilateral ureteral obstruction (UUO) is an established experimental model of renal interstitial inflammation. In our previous study, we postulated that L-selectin on monocytes is involved in their infiltration into the interstitium by UUO and that a sulfated glycolipid, sulfatide, is the physiological L-selectin ligand in the kidney. Here we tested the above hypothesis using sulfatide- and L-selectin-deficient mice. Sulfatide-deficient mice were generated by gene targeting of the cerebroside sulfotransferase (Cst) gene. Although the L-selectin-IgG chimera protein specifically bound to sulfatide fraction in acidic lipids from wild-type kidney, it did not show such binding in fractions of Cst(-/-) mice kidney, indicating that sulfatide is the major L-selectin-binding glycolipid in the kidney. The distribution of L-selectin ligand in wild-type mice changed after UUO; sulfatide was relocated from the distal tubules to the peritubular capillaries where monocytes infiltrate, suggesting that sulfatide relocated to the endothelium after UUO interacted with L-selectin on monocytes. In contrast, L-selectin ligand was not detected in Cst(-/-) mice irrespective of UUO treatment. Compared with wild-type mice, Cst(-/-) mice showed a considerable reduction in the number of monocytes/macrophages that infiltrated the interstitium after UUO. The number of monocytes/macrophages was also reduced to a similar extent in L-selectin(-/-) mice. Our results suggest that sulfatide is a major L-selectin-binding molecule in the kidney and that the interaction between L-selectin and sulfatide plays a critical role in monocyte infiltration into the kidney interstitium.

Sulfatides: targets for anti-phospholipid antibodies

BACKGROUND

Sulfatides are sulfated glycosphingolipids expressed on the surface of erythrocytes, leukocytes, and platelets. Sulfatides interact with several cell adhesion molecules involved in hemostasis. Beta2-glycoprotein I is an anionic phospholipid-binding plasma protein, and the phospholipid-bound form is the target for most anti-phospholipid antibodies that are associated with recurrent thrombosis, miscarriages, and neurological symptoms. In this study, we examined whether beta2-glycoprotein I forms a complex with sulfatides and thereby becomes a target for anti-phospholipid antibodies.

METHODS AND RESULTS

Beta2-glycoprotein I binds to surface-bound sulfatides but not to other glycolipids, such as ceramide, cerebrosides, sphingomyelin, or ganglioside. At a sulfatide coating density of 1 microg/well, beta2-glycoprotein I reaches half-maximal binding at 2.5 microg/mL, and the binding is saturated at 10 microg/mL. The binding of beta2-glycoprotein I also depends on the coating density of sulfatides in the well. At a constant beta2-glycoprotein I concentration of 5 microg/mL, maximal binding of beta2-glycoprotein I is observed at a coating density of 1 mug/well. The serum from 14 patients with anti-cardiolipin antibodies, a subset of anti-phospholipid antibodies, bound to sulfatide-bound beta2-glycoprotein I and previous absorption on cardiolipin-coated surfaces decreased the immunoreactivity toward sulfatide-beta2-glycoprotein I complex by >50% in 12 of 14 patients. Furthermore, immunoaffinity-purified anti-cardiolipin antibodies from 4 of 5 patients reacted with sulfatide-bound beta2-glycoprotein I.

CONCLUSIONS

These results show that not only anionic phospholipids, as commonly known, but also sulfatides are targets for most anti-phospholipid antibodies. We therefore postulate that interactions of these antibodies with sulfatides may contribute to some of the clinical symptoms of the anti-phospholipid antibody syndrome.

Seminolipid and its precursor/degradative product, galactosylalkylacylglycerol, in the testis of saposin A- and prosaposin-deficient mice

Sphingolipid activator proteins (saposins A, B, C, and D) are derived from a common precursor protein (prosaposin) and specifically activate in vivo degradation of glycolipids with short carbohydrate chains. A mouse model of prosaposin deficiency (prosaposin-/-) closely mimics the human disease with an elevation of multiple glycolipids. The recently developed saposin A-/- mice showed a chronic form of globoid cell leukodystrophy, establishing the essential in vivo role of saposin A as an activator for galactosylceramidase to degrade galactosylceramide. Seminolipid, the principal glycolipid in spermatozoa, and its precursor/degradative product, galactosylalkylacylglycerol (GalEAG), were analyzed in the testis of the two mouse mutants by electrospray ionization mass spectrometry. Saposin A-/- mice showed the normal seminolipid level, while that of prosaposin-/- mice was approximately 150% of the normal level at the terminal stage. In contrast, GalEAG increased up to 10 times in saposin A-/- mice, whereas it decreased with age in the wild-type as well as in prosaposin-/- mice. These analytical findings on the two saposin mutants may shed some light on the physiological function of seminolipid and GalEAG.

Inactivation of ether lipid biosynthesis causes male infertility, defects in eye development and optic nerve hypoplasia in mice

Although known for almost 80 years, the physiological role of plasmalogens (PLs), the major mammalian ether lipids (ELs), is still enigmatic. Humans that lack ELs suffer from rhizomelic chondrodysplasia punctata (RCDP), a peroxisomal disorder usually resulting in death in early childhood. In order to learn more about the functions of ELs, we generated a mouse model for RCDP by a targeted disruption of the dihydroxyacetonephosphate acyltransferase gene. The mutant mice revealed multiple abnormalities, such as male infertility, defects in eye development, cataract and optic nerve hypoplasia, some of which were also observed in RCDP. Mass spectroscopic analysis demonstrated the presence of highly unsaturated fatty acids including docosahexaenoic acid (DHA) in brain PLs and the occurrence of PLs in lipid raft microdomains (LRMs) isolated from brain myelin. In mutants, PLs were completely absent and the concentration of brain DHA was reduced. The marker proteins flotillin-1 and F3/contactin were found in brain LRMs in reduced concentrations. In addition, the gap junctional protein connexin 43, known to be recruited to LRMs and essential for lens development and spermatogenesis, was down-regulated in embryonic fibroblasts of the EL-deficient mice. Free cholesterol, an important constituent of LRMs, was found in these fibroblasts to be accumulated in a perinuclear compartment. These data suggest that the EL-deficient mice allow the identification of new phenotypes not related so far to EL-deficiency (male sterility, defects in myelination and optic nerve hypoplasia) and indicate that PLs are required for the correct assembly and function of LRMs.

Internal residue loss produced by rearrangement of a novel cationic glycosphingolipid, glyceroplasmalopsychosine, in collision-induced dissociation

A novel plasmal conjugate of galactosylsphingosine (psychosine), Gro1(3)-O-plasmal-O-6Galbeta-sphingosine (glyceroplasmalopsychosine), was analyzed by electrospray ionization and liquid secondary ion mass spectrometry with low- or high-energy collision-induced dissociation (CID). In the product ion spectra of the [M + H](+) ions, [M + H - glycerol](+) ions arising from the loss of a glycerol were predominant. Unexpectedly, CID of the [M + H - glycerol](+) ion produced an outstanding ion, [(M + H - glycerol) - Hex](+), which required the loss of the galactose from inside the molecule. This ion was greatly reduced in the spectra of N,N-dimethyl derivatives, indicating that the [(M + H - glycerol) - Hex](+) ion is formed from an intramolecular rearrangement with migration of the plasmal residue to the free amino group of sphingosine. It would be expected that the rearrangement occurs simultaneously with the elimination of glycerol or a rearranged [M + H](+) ion leads to the elimination of glycerol, to form a Schiff base-type [M + H - glycerol](+) ion, from which the terminal galactose could be removed by the normal mechanism of glycosidic cleavage. On the other hand, the [M + Na - glycerol](+) ion derived from the sodiated molecule did not produce an ion corresponding to the rearrangement reaction, possibly owing to a higher stability of the sodiated ions against conformational changes.

Galactocerebrosides are required postnatally for stromal-dependent bone marrow lymphopoiesis

Galactocerebrosides (GCs) represent a major class of glycolipids in the nervous system. Here, we show that mice lacking the key enzyme to generate GCs, UDP-galactose:ceramide galactosyltransferase (CGT(-/-)), exhibit severe postnatal atrophy of all lymphoid organs, owing to a maturational arrest before the pro-B/T cell stage. This lineage-specific defect originates from the bone marrow (BM) stroma since it is not transplantable to irradiated wild-type recipients. Remarkably, CGT(-/-) long-term B lymphoid BM cultures displayed severe deficits in the number of CD45(neg)VCAM-1(pos) stromal cells and fibronectin matrix assembly, and produced floating macrophages rather than B lymphocytes. The fibronectin network was also altered in the CGT-deficient BM parenchyma. These results point to an essential role for galactolipids in the formation of fibronectin-enriched lymphoid-specific stromal niches in the BM.

Developmental expression of the type I diabetes related antigen sulfatide and sulfated lactosylceramide in mammalian pancreas

Previous studies have shown that sulfatide is present and functionally involved in beta cells, and that anti-sulfatide antibodies (ASA) exist during development of type I diabetes mellitus. To further explore the possible role of sulfatide in type I diabetes, developmental expression was examined in human pancreas and in pancreas of the type I diabetes models BB rat and NOD mouse compared to Lewis rat and BALB/c mouse, respectively. Sulfatide was not only expressed in adult pancreas, but also in human fetal and rodent neonatal pancreas, i.e., during the growing period of the immunological self. Sulfatide had a different expression pattern in human beings and rodents, concerning both the amounts of sulfatide and expression during development. There was no change in the sulfatide fatty acid isoform expression during development. The pancreatic expression of another sulfated glycosphingolipid, sulfated lactosylceramide, indicated that this molecule is a potential fetal/neonatal marker, which was further expressed in the type I diabetic models. In conclusion, these findings give further support to the possibility that sulfatide is a relevant autoantigen in type I diabetes and that sulfated lactosylceramide might function as a potential risk factor for disease development, at least in the animal models.

Novel role for apolipoprotein E in the central nervous system. Modulation of sulfatide content

It has long been postulated that apolipoprotein E (apoE) may play a role in lipid metabolism in the brain. However, direct evidence that apoE plays such a role is lacking. We investigated whether apoE isoforms influence lipid content in the brain. We compared the brains of wild-type mice to apoE knockout (-/-) and human apoE3 and apoE4 transgenic mice and compared cerebrospinal fluid (CSF) of humans with different apoE isoforms. We found that there was no effect of apoE on the content of multiple phospholipids, sphingolipids, and cholesterol. There was, however, a marked effect of apoE on the sulfatide (ST) content in both the brain and CSF. The sulfatide mass in hippocampus and cortex of apoE knockout mice was found to be 61 and 114 mol% higher than wild-type mice counterparts at 12 months of age. In contrast, the sulfatide content in brain tissues from human apoE4-expressing mice was approximately 60% less than those found in wild-type mice of the same age. The ST mass in human CSF was significantly dependent on the APOE genotypes of the subjects. Examination of potential sulfatide carrier(s) in human CSF demonstrated that sulfatides are specifically associated with apoE-containing high density lipoproteins, suggesting that sulfatide levels in the central nervous system (CNS) are likely to be directly modulated by the same metabolic pathways that regulate levels of apoE-containing CNS lipoproteins. This novel role for apoE in the CNS may provide new insights into the connection of apoE with Alzheimer's disease and poor recovery after brain injury.

Sulfatide and GM1 ganglioside modulate the high-affinity dopamine uptake in rat striatal synaptosomes: evidence for the involvement of their ionic charges

The present study was undertaken to examine the effects of the anionic glycolipids GM1 ganglioside and sulfatide on the high-affinity dopamine (DA) uptake in rat striatal synaptosomes. After 1h of incubation, GM1 stably bound to synaptosomes and modified the activity of the neuronal dopamine transporter (DAT). With 1.2 and 12 microM GM1, V(max) decreased by 13 and 23%, respectively, reflecting a slight reduction of the number of functional uptake sites and K(m) was lowered by 21 and 33%, thus showing an increase of the affinity. Treatment of synaptosomes with 1.2 microM of sulfatide, which possesses an anionic sulfated group, led to a similar decrease of V(max) (19%) than GM1, but to a significantly higher reduction of K(m) (35%). In fact, sulfatide associated to synaptosomes in a 3.5-fold higher extent than GM1. Conversely, when GM1 and sulfatide were replaced by GM1 alcohol and galactosylceramide, respectively, no modification of the DA uptake occurred, although these neutral glycolipids incorporated into the synaptosomes to the same extent as the related anionic compounds.Altogether, these results demonstrate the key role of negative charges linked to the oligosaccharide chains of glycolipids in the modulation of DA transport across the synaptosomal membrane.

Sulfotransferases and sulfated oligosaccharides

Structural diversity of the sugar chains attached to proteins and lipids that arises from the variety of combinations of different monosaccharides, different types of linkages, branch formation and secondary modifications, such as sulfation, possesses a large amount of biological information. A number of proteoglycans, glycoproteins, and glycolipids contain sulfated carbohydrates. Their sulfate groups provide a negative charge and play a role in a specific molecular recognition process. The sulfation of oligosaccharides is catalyzed by the Golgi-associated sulfotransferases. Recent success in molecular cloning of these sulfotransferases has brought a breakthrough in the understanding of biological function of sulfated oligosaccharides in a variety of contexts. Investigations on the relationship of sulfated oligosaccharides to human diseases including hereditary deficiency, cancer, inflammation, and infection may provide hints for curing disastrous diseases.

Substantial sulfatide deficiency and ceramide elevation in very early Alzheimer's disease: potential role in disease pathogenesis

In addition to pathology in the gray matter, there are also abnormalities in the white matter in Alzheimer's disease (AD). Sulfatide species are a class of myelin-specific sphingolipids and are involved in certain diseases of the central nervous system. To assess whether sulfatide content in gray and white matter in human subjects is associated with both the presence of Alzheimer's disease (AD) pathology as well as the stage of dementia, we analyzed the sulfatide content of brain tissue lipid extracts by electrospray ionization mass spectrometry from 22 subjects whose cognitive status at time of death varied from no dementia to very severe dementia. All subjects with dementia had AD pathology. The results demonstrate that: (i) sulfatides were depleted up to 93% in gray matter and up to 58% in white matter from all examined brain regions from AD subjects with very mild dementia, whereas all other major classes of lipid (except plasmalogen) in these subjects were not altered in comparison to those from age-matched subjects with no dementia; (ii) there was no apparent deficiency in the biosynthesis of sulfatides in very mild AD subjects as characterized by the examination of galactocerebroside sulfotransferase activities in post-mortem brain tissues; (iii) the content of ceramides (a class of potential degradation products of sulfatides) was elevated more than three-fold in white matter and peaked at the stage of very mild dementia. The findings demonstrate that a marked decrease in sulfatides is associated with AD pathology even in subjects with very mild dementia and that these changes may be linked with early events in the pathological process of AD.

Kidney sulfatides in mouse models of inherited glycosphingolipid disorders: determination by nano-electrospray ionization tandem mass spectrometry

Sulfatides show structural, and possibly physiological similarities to gangliosides. Kidney dysfunction might be correlated with changes in sulfatides, the major acidic glycosphingolipids in this organ. To elucidate their in vivo metabolic pathway these compounds were analyzed in mice afflicted with inherited glycosphingolipid disorders. The mice under study lacked the genes encoding either beta-hexosaminidase alpha-subunit (Hexa-/-), the beta-hexosaminidase beta-subunit (Hexb-/-), both beta-hexosaminidase alpha and beta-subunits (Hexa-/- and Hexb-/-), GD3 synthase (GD3S-/-), GD3 synthase and GalNAc transferase (GD3S-/- and GalNAcT-/-), GM2 activator protein (Gm2a-/-), or arylsulfatase A (ASA-/-). Quantification of the sulfatides, I(3)SO(3)(-)-GalCer (SM4s), II(3)SO(3)(-)-LacCer (SM3), II(3)SO(3)(-)-Gg(3)Cer (SM2a), and IV(3,) II(3)-(SO(3)(-))(2)-Gg(4)Cer (SB1a), was performed by nano-electrospray tandem mass spectrometry. We conclude for the in vivo situation in mouse kidneys that: 1) a single enzyme (GalNAc transferase) is responsible for the synthesis of SM2a and GM2 from SM3 and GM3, respectively. 2) In analogy to GD1a, SB1a is degraded via SM2a. 3) SM2a is hydrolyzed to SM3 by beta-hexosaminidase S (Hex S) and Hex A, but not Hex B. Both enzymes are supported by GM2-activator protein. 4) Arylsulfatase A is required to degrade SB1a. It is probably the sole sphingolipid-sulfatase cleaving the galactosyl-3-sulfate bond. In addition, a human Tay-Sachs patient's liver was investigated, which showed accumulation of SM2a along with GM2 storage. The different ceramide compositions of both compounds indicated they were probably derived from different cell types. These data demonstrate that in vivo the sulfatides of the ganglio-series follow the same metabolic pathways as the gangliosides with the replacement of sulfotransferases and sulfatases by sialyltransferases and sialidases. Furthermore, a novel neutral GSL, IV(6)GlcNAcbeta-Gb(4)Cer, was found to accumulate only in Hexa-/- and Hexb-/- mouse kidneys. From this we conclude that Hex S also efficiently cleaves terminal beta1-6-linked HexNAc residues from neutral GSLs in vivo.

Binding of arylsulfatase A to mouse sperm inhibits gamete interaction and induces the acrosome reaction

We have shown previously that male germ cell-specific sulfoglycolipid, sulfogalactosylglycerolipid (SGG), is involved in sperm-zona pellucida binding, and that SGG and its desulfating enzyme, arylsulfatase A (AS-A), coexist in the same sperm head area. However, AS-A exists at a markedly low level in sperm as compared to SGG (i.e., 1/400 of SGG molar concentration). In the present study, we investigated whether perturbation of this molar ratio would interfere with sperm-egg interaction. We demonstrated that purified AS-A bound to the mouse sperm surface through its high affinity with SGG. When capacitated, Percoll gradient-centrifuged mouse sperm were treated for 1 h with various concentrations of AS-A, their binding to zona-intact eggs was inhibited in a dose-dependent manner and reached the background level with 63 nM AS-A. This inhibition could be partially explained by an increase in premature acrosome reaction. The acrosome-reacted sperm population of the 63 nM AS-A-treated sperm sample was twice that of the control sample (treated with 63 nM ovalbumin) at 1 h (i.e., 32% vs. 15%) and rose to 53% at 2 h. This induction was presumably due to SGG aggregation attributed to AS-A, existing as a dimer at neutral pH, and could be mimicked by anti-SGG immunoglobulin (Ig) G/IgM + secondary IgG antibody. Drastic inhibition (75%) of in vivo fertilization was also observed in females inseminated with sperm suspension containing 630 nM AS-A as compared to the rate in females inseminated with sperm suspension included with 630 nM ovalbumin. Our results demonstrate a promising potential for AS-A as a nonhormonal, vaginal contraceptive.

Paranodal junction formation and spermatogenesis require sulfoglycolipids

Mammalian sulfoglycolipids comprise two major members, sulfatide (HSO3-3-galactosylceramide) and seminolipid (HSO3-3-monogalactosylalkylacylglycerol). Sulfatide is a major lipid component of the myelin sheath and serves as the epitope for the well known oligodendrocyte-marker antibody O4. Seminolipid is synthesized in spermatocytes and maintained in the subsequent germ cell stages. Both sulfoglycolipids can be synthesized in vitro by using the isolated cerebroside sulfotransferase. To investigate the physiological role of sulfoglycolipids and to determine whether sulfatide and seminolipid are biosynthesized in vivo by a single sulfotransferase, Cst-null mice were generated by gene targeting. Cst(-/-) mice lacked sulfatide in brain and seminolipid in testis, proving that a single gene copy is responsible for their biosynthesis. Cst(-/-) mice were born healthy, but began to display hindlimb weakness by 6 weeks of age and subsequently showed a pronounced tremor and progressive ataxia. Although compact myelin was preserved, Cst(-/-) mice displayed abnormalities in paranodal junctions. On the other hand, Cst(-/-) males were sterile because of a block in spermatogenesis before the first meiotic division, whereas females were able to breed. These data show a critical role for sulfoglycolipids in myelin function and spermatogenesis.

Sulfogalactosylglycerolipid is involved in human gamete interaction

Recent results from our laboratory have revealed the role of sulfogalactosylglycerolipid (SGG) in mouse sperm-zona pellucida (ZP) binding. In this report, we demonstrated the presence of SGG in Percoll-gradient centrifuged (PGC) human sperm by high performance thin layer chromatography with orcinol and Azure A staining, specific for glycolipids and sulfolipids, respectively. SGG in human PGC sperm was quantified by its affinity to Azure A to be 12-15 mol% of sperm lipids. Indirect immunofluorescence revealed that SGG existed on both live and aldehyde fixed human sperm in the head region. Pretreatment of human PGC sperm with affinity purified antiSGG Fab markedly inhibited sperm binding to the ZP in a concentration dependent manner, without any changes in the spontaneous acrosome rate or sperm motility parameters. Fluorescently labeled SGG liposomes also bound uniformly to isolated human ZP, while fluorescently labeled galactosylglycerolipid (GG, SGG's parental lipid) or phosphatidylserine (PS, negatively charged like SGG) liposomes did not. All of these results suggested the role of human sperm SGG in ZP binding.

The aglycone of sulfogalactolipids can alter the sulfate ester substitution position required for hsc70 recognition

3'-Sulfogalactolipids(SGLs), sulfogalactosyl ceramide (SGC), and sulfogalactoglycerolipid (SGG) bind to the N-terminal ATPase-containing domain of members of the heat shock protein 70 family. We have probed this binding specificity using a series of synthetic positional sulfated or phosphorylated glycolipid analogues, containing either a long-chain bisalkyl hydrocarbon-2-(tetradecyl)hexadecane (B30) or C(18) ceramide (SGC(18)) backbone. By TLC overlay and receptor ELISA, recombinant hsc70 bound ceramide-based glycoconjugates having 3'- or 4'-sulfogalactose glycone moieties and the 4'-sulfogalactose positional isomer conjugated to B30. Hsc70 binding was significantly decreased to the 3'-sulfogalactose conjugated to the long-chain branched alkane. 3'-Sulfoglucose conjugated to B30 was not bound, nor were similarly conjugated di-, tri-, and tetra-sulfated or phosphorylated galactolipids. These results highlight the importance of the position, rather than the number of sulfate esters within the galactose ring. This binding selectivity was shared by the sea urchin hsp70-related sperm receptor. A 3'-SGC-based soluble inhibitor, in which the acyl chain was replaced with an adamantyl group, inhibited binding of hsc70 to both 3'- and 4'-SGC species with an IC(50) of 50 and 75 microM, respectively, indicating a shared sulfogalactose binding site. These studies demonstrate the highly specific nature of hsc70/SGL binding and show, for the first time, that the lipid aglycone can alter the substitution position requirement for glycolipid recognition.

Anti-SLIP1-reactive proteins exist on human spermatozoa and are involved in zona pellucida binding

Sulpholipid immobilizing protein 1 (SLIP1) is an evolutionarily conserved 68 kDa plasma membrane protein, present selectively in germ cells. We have previously shown that mouse sperm SLIP1 is involved in sperm-zona pellucida (ZP) binding. In this report, we extended our study to the human system. Immunoblotting demonstrated that anti-SLIP1-reactive proteins (mol. wt 68 and 48 kDa) could be extracted from human spermatozoa by an ATP-containing solution, a result that is consistent with observations in other species. Direct immunofluorescence, using Cy3-conjugated anti-SLIP1 IgG, revealed SLIP1 staining over the acrosomal region, with higher intensity at the posterior area. Using the human sperm-ZP binding assay, we demonstrated that pretreatment of human spermatozoa from three donors with anti-SLIP1 IgG revealed lower numbers of zona-bound spermatozoa, as compared to the corresponding control spermatozoa treated with normal rabbit serum IgG. This decrease in zona pellucida binding was not from an antibody-induced decline in sperm motility or an increase in the premature acrosome reaction. The results strongly suggest that anti-SLIP-reactive proteins on human spermatozoa play an important role in ZP binding.

Suppression of integrin expression and tumorigenicity by sulfation of lactosylceramide in 3LL Lewis lung carcinoma cells

To investigate the cellular functions of sulfated glycosphingolipids, we introduced the cerebroside sulfotransferase (CST) gene into J5 cells, a subclone of 3LL Lewis lung carcinoma cells. The J5 cells lack acidic glycosphingolipids but accumulate their common biosynthetic precursor, lactosylceramide. We established the stable CST transfectants, J5/CST-1 and J5/CST-2 clones, highly expressing sulfated lactosylceramide (SM3). Both clones exhibited more spherical morphology in comparison to mock transfectant, and their adhesiveness to fibronectin and laminin was significantly lower. The loss of cell-substratum interactions in these SM3-expressing cells could be attributed to decreased expression of integrins (alpha(5), alpha(6), and beta(1)) on the cell surface and their whole cellular levels. However, the levels of H-2K(b) and H-2D(b) antigens remained unchanged. Reverse transcriptase-polymerase chain reaction and Northern blot analyses for these integrins exhibited significant decrease of beta(1) gene expression in J5/CST-1 and 2, but there was no change in the levels of alpha(5) and alpha(6) transcripts. Deglycosylation by endoglycosidase H treatment clearly demonstrated that the precursor form of beta(1) integrin, possessing high mannose oligosaccharide chains, was preferentially decreased in the CST transfectants. These results demonstrate that endogenous SM3 negatively regulates beta(1) integrin expression at the transcriptional level, and the decrease of alpha integrin proteins in the CST transfectants was due to the post-transcriptional modification. We suggest the putative importance of the intracellular pre-beta(1) integrin pool for normal integrin maturation and subsequent function. Although the rates of cell proliferation in vitro for mock and CST transfectants were similar, tumorigenicity of J5/CST-1 and -2 cells inoculated into syngeneic C57/BL6 mice was greatly decreased or even absent. This was probably due to global loss of the efficient cell-matrix interactions, which are essential for the development of malignant tumors in vivo. Thus, we showed the evidence that cellular SM3 negatively regulates the cell-substratum interaction, resulting in the loss of tumorigenicity.

Lead exposure affects levels of galactolipid metabolic enzymes in the developing rat brain

Lead poisoning is known to cause myelin defects. Galactolipids are the major lipid components of myelin and myelin-competent oligodendrocytes. The present study examines the cellular activity of enzymes involved in the galactolipid pathway, tissue concentrations of galactolipids, and the cellular activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) in rat pups exposed to lead in utero and subsequently through maternal milk from exposed mothers and in drinking water following weaning. Pups from control and lead-treated groups (500 or 2000 ppm lead in the drinking water) were euthanized by decapitation on postnatal day 7, 14, 21, 35, or 56. Lead decreased levels of galactolipids and the oligodendrocyte marker CNPase in the brain to a similar degree. The ratios of galactocerebrosides/sulfatides and nonhydroxy fatty acid/hydroxy fatty acid forms of the galactolipids were not altered by lead treatment. In contrast, the activities of the galactolipid metabolic enzymes were reduced to a degree significantly greater than that of CNPase or galactolipids. These results are consistent with previously obtained data indicating that in vitro cultured oligodendroglial progenitor cells are a target for Pb toxicity. Chronic Pb exposure may impact on brain development by impairing timely myelin production due to perturbation of the early developmental commitment of oligodendroglial progenitors. It is further suggested that perturbation of the galactolipid pathway during the developmental maturation of oligodendrocytes may represent a contributing mechanism for Pb-induced neurotoxicity.

Roles of galactose and sulfate residues in sulfatides for their antagonistic functions in the blood coagulation system

We previously reported that the sulfatide (galactosylceramide I3-sulfate) may have contradictory functions, namely both coagulant and anticoagulant roles in vivo: sulfatide induced giant thrombi formation when injected into rats with vein ligation, whereas no thrombi were formed when sulfatide was injected into rats without vein ligation. Rather it prolonged bleeding time. To investigate the structural features of sulfatide for both functions, a synthetic sulfatide (galactosylceramide I6-sulfate) which does not occur naturally, cholesterol 3-sulfate and ganglioside GM4 were examined together with naturally occurring sulfatide. Both sulfatides and cholesterol 3-sulfate induced giant thrombi in the rats with vein ligation within ten minutes of injection, although cholesterol 3-sulfate exhibited weaker coagulant activity than the sulfatides. On the contrary, both sulfatides significantly prolonged bleeding time but cholesterol 3-sulfate barely prolonged it when injected without vein ligation. GM4 exhibited neither coagulant nor anticoagulant activity. These results suggested that sulfate moiety in the sulfatides is essential for coagulant activity and that galactose residue enhances the activity, whereas both galactose and sulfate residues seem to be important for anticoagulant activity. This is because the sulfatides possess both residues but GM4 possesses galactose without sulfate and cholesterol 3-sulfate possesses sulfate without galactose. We previously reported that the possible mechanism of anticoagulation by sulfatide was due to its binding to fibrinogen, thereby inhibiting the conversion to fibrin. In this paper we reveal that both sulfatides inhibited thrombin activity independent of heparin cofactor II, thus providing evidence of another anticoagulation mechanism for the sulfatides.

The ATPase domain of hsp70 possesses a unique binding specificity for 3'-sulfogalactolipids

The region(s) of hsp70 critical for sulfogalactolipid (SGL) recognition has been defined through deletion analysis and site-directed mutagenesis. Truncated polymerase chain reaction products of hsp70 generated N-terminal fragments of 43, 35, 29, and 22 kDa. The C terminus substrate-binding domain (28 kDa) was also expressed. The N-terminal ATPase domain (rP43) shared the binding specificity of hsp70, because only sulfogalactosyl ceramide and sulfogalactosyl glycerolipid were recognized by both TLC overlay and RELISA. The C-terminal domain showed no binding. SGL binding of rP29 and rP22 was severely reduced. The loss of SGL binding for rP35 by RELISA but not TLC overlay was considered as a function of receptor presentation. The truncation of rP43 to rP35 demonstrates that residues 318-387 (the base of the ATP binding cleft) are critical for high affinity SGL binding. Mutagenesis showed that Arg(342) and Phe(198) are crucial for this process. SGL binding, mediated by these conserved residues within the ATPase domain of hsp70, implies that this binding specificity is evolutionarily conserved.

Conformational studies on a unique bis-sulfated glycolipid using NMR spectroscopy and molecular dynamics simulations

The time-averaged solution conformation of a unique bis-sulfated glycolipid (HSO3)2-2,6Manalpha-2Glcalpha-1-sn-2,3-O-alkylglycerol , was studied in terms of the torsional angles of two glycosidic linkages, phi (H1-C1-O-Cx) and psi (C1-O-Cx-Hx), derived from heteronuclear three-bond coupling constants (3JC,H), and inter-residual proton-proton distances from J-HMBC 2D and ROESY experiments, respectively. The dihedral angles of Glcalpha1Gro in glycolipids were determined for the first time. The C1-C4 diagonal line of the alpha-glucose ring makes an angle of approximately 120 degrees with the glycerol backbone, suggesting that the alpha-glucose ring is almost parallel to the membrane surface in contrast with the perpendicular orientation of the beta-isomer. Furthermore, minimum-energy states around the conformation were estimated by Monte Carlo/stochastic dynamics (MCSD) mixed-mode simulations and the energy minimization with assisted model building and energy refinement (AMBER) force field. The Glcalpha1Gro linkage has a single minimum-energy structure. On the other hand, three conformers were observed for the Manalpha2Glc linkage. The flexibility of Manalpha2Glc was further confirmed by the absence of inter-residual hydrogen bonds which were judged from the temperature coefficients of the chemical shifts, ddelta/dT (-10-3 p.p.m. degrees C-1), of hydroxy protons. The conformational flexibility may facilitate interaction of extracellular substances with both sulfate groups.