A carbohydrate-carbohydrate interaction between galactosylceramide-containing liposomes and cerebroside sulfate-containing liposomes: dependence on the glycolipid ceramide composition

Concurrent acute sensorimotor axonal neuropathy and disseminated encephalitis associated with Chlamydia pneumoniae in an adult patient with anti-MOG and anti-sulfatide antibodies: a case report

Acute disseminated encephalomyelitis and Guillain-Barré syndrome refer to post-infectious or post-vaccination inflammatory demyelinating disorders of central and peripheral nervous system, respectively. We report the case of a 60-year-old male patient presenting with irritability, gait difficulty, asymmetric quadriparesis (mostly in his left extremities), distal sensory loss for pain and temperature in left limbs, and reduced tendon reflexes in his upper limbs and absent in his lower limbs, following an upper respiratory tract infection, 3 weeks earlier. Brain magnetic resonance imaging revealed abnormal T2 signal and peripherally enhancing lesions in hemispheres, brainstem, and cerebellum. Nerve conduction studies were compatible with acute motor and sensory axonal neuropathy. Serology revealed positive IgM and IgG antibodies for Chlamydia pneumoniae, and he also tested positive for myelin oligodendrocyte glycoprotein (MOG) and sulfatide antibodies. Treatment with intravenous immunoglobulin and methylprednisolone led to clinical and radiological recovery within weeks. Even though several cases of combined central and peripheral demyelination have been reported before, it is the first case report with seropositive anti-sulfatide and anti-MOG acute sensorimotor axonal neuropathy and disseminated encephalitis associated with C. pneumoniae.

Progress in Antiviral Fullerene Research

Unlike traditional small molecule drugs, fullerene is an all-carbon nanomolecule with a spherical cage structure. Fullerene exhibits high levels of antiviral activity, inhibiting virus replication in vitro and in vivo. In this review, we systematically summarize the latest research regarding the different types of fullerenes investigated in antiviral studies. We discuss the unique structural advantage of fullerenes, present diverse modification strategies based on the addition of various functional groups, assess the effect of structural differences on antiviral activity, and describe the possible antiviral mechanism. Finally, we discuss the prospective development of fullerenes as antiviral drugs.

Sulfatide with ceramide composed of phytosphingosine (t18:0) and 2-hydroxy fatty acids in renal intercalated cells

Diverse molecular species of sulfatide with differences in FA lengths, unsaturation degrees, and hydroxylation statuses are expressed in the kidneys. However, the physiological functions of specific sulfatide species in the kidneys are unclear. Here, we evaluated the distribution of specific sulfatide species in the kidneys and their physiological functions. Electron microscopic analysis of kidneys of Cst-deficient mice lacking sulfatide showed vacuolar accumulation in the cytoplasm of intercalated cells in the collecting duct, whereas the proximal and distal tubules were unchanged. Immunohistochemical analysis revealed that vacuolar H⁺-ATPase-positive vesicles were accumulated in intercalated cells in sulfatide-deficient kidneys. Seventeen sulfatide species were detected in the murine kidney by iMScope MALDI-MS analysis. The distribution of the specific sulfatide species was classified into four patterns. Although most sulfatide species were highly expressed in the outer medullary layer, two unique sulfatide species of m/z 896.6 (predicted ceramide structure: t18:0-C22:0h) and m/z 924.6 (predicted ceramide structure: t18:0-C24:0h) were dispersed along the collecting duct, implying expression in intercalated cells. In addition, the intercalated cell-enriched fraction was purified by fluorescence-activated cell sorting using the anti-vacuolar H⁺-ATPase subunit 6V0A4, which predominantly contained sulfatide species (m/z 896.6 and 924.6). The Degs2 and Fa2h genes, which are responsible for ceramide hydroxylation, were expressed in the purified intercalated cells. These results suggested that sulfatide molecular species with ceramide composed of phytosphingosine (t18:0) and 2-hydroxy FAs, which were characteristically expressed in intercalated cells, were involved in the excretion of NH₃ and protons into the urine.

A metabolome atlas of the aging mouse brain

The mammalian brain relies on neurochemistry to fulfill its functions. Yet, the complexity of the brain metabolome and its changes during diseases or aging remain poorly understood. Here, we generate a metabolome atlas of the aging wildtype mouse brain from 10 anatomical regions spanning from adolescence to old age. We combine data from three assays and structurally annotate 1,547 metabolites. Almost all metabolites significantly differ between brain regions or age groups, but not by sex. A shift in sphingolipid patterns during aging related to myelin remodeling is accompanied by large changes in other metabolic pathways. Functionally related brain regions (brain stem, cerebrum and cerebellum) are also metabolically similar. In cerebrum, metabolic correlations markedly weaken between adolescence and adulthood, whereas at old age, cross-region correlation patterns reflect decreased brain segregation. We show that metabolic changes can be mapped to existing gene and protein brain atlases. The brain metabolome atlas is publicly available ( https://mouse.atlas.metabolomics.us/ ) and serves as a foundation dataset for future metabolomic studies.

Sphingolipids: membrane microdomains in brain development, function and neurological diseases

Sphingolipids are highly enriched in the nervous system where they are pivotal constituents of the plasma membranes and are important for proper brain development and functions. Sphingolipids are not merely structural elements, but are also recognized as regulators of cellular events by their ability to form microdomains in the plasma membrane. The significance of such compartmentalization spans broadly from being involved in differentiation of neurons and synaptic transmission to neuronal–glial interactions and myelin stability. Thus, perturbations of the sphingolipid metabolism can lead to rearrangements in the plasma membrane, which has been linked to the development of various neurological diseases. Studying microdomains and their functions has for a long time been synonymous with studying the role of cholesterol. However, it is becoming increasingly clear that microdomains are very heterogeneous, which among others can be ascribed to the vast number of sphingolipids. In this review, we discuss the importance of microdomains with emphasis on sphingolipids in brain development and function as well as how disruption of the sphingolipid metabolism (and hence microdomains) contributes to the pathogenesis of several neurological diseases.

Nimodipine but Not Nifedipine Promotes Expression of Fatty Acid 2-Hydroxylase in a Surgical Stress Model Based on Neuro2a Cells

Nimodipine is well characterized for the management of aneurysmal subarachnoid hemorrhage and has been shown to promote a better outcome and less delayed ischemic neurological deficits. Animal and clinical trials show neuroprotective efficacy following nerve injuries. We showed a neuroprotective effect on Neuro2a cells. Subsequent microarray analysis revealed—among others—fatty acid 2-hydroxylase (FA2H) upregulated by nimodipine in vitro, which is a component of myelin synthesis. Differentiated Neuro2a cells were analyzed for nimodipine-mediated survival considering stress treatment in comparison to nifedipine-treatment. Cell survival was determined by measurement of LDH activity in the culture medium. Nimodipine decreased surgery-like stress-induced cell death of differentiated Neuro2a cells. Neuro2a cell culture was analyzed for changes in FA2H expression induced by nimodipine or nifedipine in surgery-like stress conditions. We analyzed expression levels of FA2H mRNA and protein by qPCR using fa2h specific primers or a FA2H-specific antibody in nimodipine or nifedipine non- and pre-treated Neuro2a cell culture, respectively. Nimodipine but not nifedipine increases FA2H protein levels and also significantly increases mRNA levels of FA2H in both undifferentiated and differentiated Neuro2a cells. Our findings indicate that higher expression of FA2H induced by nimodipine may cause higher survival of Neuro2a cells stressed with surgery-like stressors.

Sulfatide species with various fatty acid chains in oligodendrocytes at different developmental stages determined by imaging mass spectrometry

HSO3-3-galactosylceramide (Sulfatide) species comprise the major glycosphingolipid components of oligodendrocytes and myelin and play functional roles in the regulation of oligodendrocyte maturation and myelin formation. Although various sulfatide species contain different fatty acids, it is unclear how these sulfatide species affect oligodendrogenesis and myelination. The O4 monoclonal antibody reaction with sulfatide has been widely used as a useful marker for oligodendrocytes and myelin. However, sulfatide synthesis during the pro-oligodendroblast stage, where differentiation into the oligodendrocyte lineage has already occurred, has not been examined. Notably, this stage comprises O4-positive cells. In this study, we identified a sulfatide species from the pro-oligodendroblast-to-myelination stage by imaging mass spectrometry. The results demonstrated that short-chain sulfatides with 16 carbon non-hydroxylated fatty acids (C16) and 18 carbon non-hydroxylated fatty acids (C18) or 18 carbon hydroxylated fatty acids (C18-OH) existed in restricted regions of the early embryonic spinal cord, where pro-oligodendroblasts initially appear, and co-localized with Olig2-positive pro-oligodendroblasts. C18 and C18-OH sulfatides also existed in isolated pro-oligodendroblasts. C22-OH sulfatide became predominant later in oligodendrocyte development and the longer C24 sulfatide was predominant in the adult brain. Additionally, the presence of each sulfatide species in a different area of the adult brain was demonstrated by imaging mass spectrometry at an increased lateral resolution. These findings indicated that O4 recognized sulfatides with short-chain fatty acids in pro-oligodendroblasts. Moreover, the fatty acid chain of the sulfatide became longer as the oligodendrocyte matured. Therefore, individual sulfatide species may have unique roles in oligodendrocyte maturation and myelination. Read the Editorial Highlight for this article on page 356.

Carbohydrate-to-carbohydrate interactions between α2,3-linked sialic acids on α2 integrin subunits and asialo-GM1 underlie the bone metastatic behaviour of LNCAP-derivative C4-2B prostate cancer cells

Complex interplays among proteins, lipids and carbohydrates can alter the phenotype and are suggested to have a crucial role in tumour metastasis. Our previous studies indicated that a complex of the GSLs (glycosphingolipids), AsGM1 (asialo-GM1), which lacks α2,3-linked sialic acid, and α2β1 integrin receptors is responsible for the metastatic behaviour of C4-2B prostate cancer cells. Herein, we identified and addressed the functional significance of changes in sialylation during prostate cancer progression. We observed an increase in α2,3-linked sialic acid residues on α2 subunits of α2β1 integrin receptors, correlating with increased gene expression of α2,3-STs (sialyltransferases), particularly ST3GAL3. Cell surface α2,3-sialylation of α2 subunits was required for the integrin α2β1-dependent cell adhesion to collagen type I and the same α2,3-linked sialic acid residues on the integrin receptor were responsible for the interaction with the carbohydrate moiety of AsGM1, explaining the complex formation between AsGM1 and α2β1 integrin receptors. These results provide novel insights into the role of sialic acids in the organization and function of important membrane components in invasion and metastatic processes.

Contribution of galactoglycerolipids to the 3-dimensional architecture of thylakoids

Thylakoid membranes, the universal structure where photosynthesis takes place in all oxygenic photosynthetic organisms from cyanobacteria to higher plants, have a unique lipid composition. They contain a high fraction of 2 uncharged glycolipids, the galactoglycerolipids mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), and an anionic sulfolipid, sulfoquinovosediacylglycerol (SQDG). A remarkable feature of the evolution from cyanobacteria to higher plants is the conservation of MGDG, DGDG, SQDG, and phosphatidylglycerol (PG), the major phospholipid of thylakoids. Using neutron diffraction on reconstituted thylakoid lipid extracts, we observed that the thylakoid lipid mixture self-organizes as a regular stack of bilayers. This natural lipid mixture was shown to switch from hexagonal II toward lamellar phase on hydration. This transition and the observed phase coexistence are modulated by the fine-tuning of the lipid profile, in particular the MGDG/DGDG ratio, and by the hydration. Our analysis highlights the critical role of DGDG as a contributing component to the membrane stacking via hydrogen bonds between polar heads of adjacent bilayers. DGDG interactions balance the repulsive electrostatic contribution of the charged lipids PG and SQDG and allow the persistence of regularly stacked membranes at high hydration. In developmental contexts or in response to environmental variations, these properties can contribute to the highly dynamic flexibility of plastid structure.

Role of galactosylceramide and sulfatide in oligodendrocytes and CNS myelin: formation of a glycosynapse

The two major glycosphingolipids of myelin, galactosylceramide (GalC) and sulfatide (SGC), interact with each other by trans carbohydrate-carbohydrate interactions in vitro. They face each other in the apposed extracellular surfaces of the multilayered myelin sheath produced by oligodendrocytes and could also contact each other between apposed oligodendrocyte processes. Multivalent galactose and sulfated galactose, in the form of GalC/SGC-containing liposomes or silica nanoparticles conjugated to galactose and galactose-3-sulfate, interact with GalC and SGC in the membrane sheets of oligodendrocytes in culture. This interaction causes transmembrane signaling, loss of the cytoskeleton and clustering of membrane domains, similar to the effects of cross-linking by anti-GalC and anti-SGC antibodies. These effects suggest that GalC and SGC could participate in glycosynapses, similar to neural synapses or the immunological synapse, between GSL-enriched membrane domains in apposed oligodendrocyte membranes or extracellular surfaces of mature myelin. Formation of such glycosynapses in vivo would be important for myelination and/or oligodendrocyte/myelin function.

2'-Hydroxy ceramide in membrane homeostasis and cell signaling

Ceramide is a precursor of complex sphingolipids and also plays important roles in cell signaling. With the advances in lipid analytical technologies, the structural diversity of ceramide species have become evident, and the complexity of cellular metabolism and function associated with distinct ceramide species is beginning to be revealed. One of the common structural variations of ceramide is 2'-hydroxylation of the N-acyl chain. Fatty acid 2-hydroxylase (FA2H) is one of the enzymes that introduce the hydroxyl group during de novo synthesis of ceramide. FA2H is essential for the normal functioning of the nervous system, as evidenced by demyelinating disorder associated with FA2H mutations in humans and mice. Studies of Fa2h mutant mice indicate that lack of 2'-hydroxy galactosylceramide in the myelin membrane results in loss of long-term stability of myelin and eventual demyelination. FA2H also regulates differentiation of various cell types (epidermal keratinocytes, schwannoma cells, adipocytes). When provided exogenously, ceramide induces apoptosis in many cell types. Interestingly, the effective concentration of 2'-hydroxy ceramide that induces apoptosis is significantly lower compared to non-hydroxy ceramide, and cells die much more rapidly, suggesting that 2'-hydroxy ceramide can mediate proapoptotic signaling distinct from non-hydroxy ceramide. Collectively, current evidence clearly shows that 2'-hydroxy ceramide and 2'-hydroxy complex sphingolipids have unique functions in membrane homeostasis and cell signaling that could not be substituted by non-hydroxy counterparts.

Ganglioside biochemistry

Gangliosides are sialic acid-containing glycosphingolipids. They occur especially on the cellular surfaces of neuronal cells, where they form a complex pattern, but are also found in many other cell types. The paper provides a general overview on their structures, occurrence, and metabolism. Key functional, biochemical, and pathobiochemical aspects are summarized.

Neutralization of B. anthracis toxins during ex vivo phagocytosis

Glycoconjugates (GCs) are recognized as stimulation and signaling agents, affecting cell adhesion, activation, and growth of living organisms. Among GC targets, macrophages are considered ideal since they play a central role in inflammation and immune responses against foreign agents. In this context, we studied the effects of highly selective GCs in neutralizing toxin factors produced by B. anthracis during phagocytosis using murine macrophages. The effects of GCs were studied under three conditions: A) prior to, B) during, and C) following exposure of macrophages to B. anthracis individual toxin (protective antigen [PA], edema factor [EF], lethal factor [LF] or toxin complexes (PA-EF-LF, PA-EF, and PA-LF). We employed ex vivo phagocytosis and post-phagocytosis analysis including direct microscopic observation of macrophage viability, and macrophage activation. Our results demonstrated that macrophages are more prone to adhere to GC-altered PA-EF-LF, PA-EF, and PA-LF toxin complexes. This adhesion results in a higher phagocytosis rate and toxin complex neutralization during phagocytosis. In addition, GCs enhance macrophage viability, activate macrophages, and stimulate nitric oxide (NO) production. The present study may be helpful in identifying GC ligands with toxin-neutralizing and/or immunomodulating properties. In addition, our study could suggest GCs as new targets for existing vaccines and the prospective development of vaccines and immunomodulators used to combat the effects of B. anthracis.

Encephalopathy caused by ablation of very long acyl chain ceramide synthesis may be largely due to reduced galactosylceramide levels

Sphingolipids (SLs) act as signaling molecules and as structural components in both neuronal cells and myelin. We now characterize the biochemical, histological, and behavioral abnormalities in the brain of a mouse lacking very long acyl (C22-C24) chain SLs. This mouse, which is defective in the ability to synthesize C22-C24-SLs due to ablation of ceramide synthase 2, has reduced levels of galactosylceramide (GalCer), a major component of myelin, and in particular reduced levels of non-hydroxy-C22-C24-GalCer and 2-hydroxy-C22-C24- GalCer. Noteworthy brain lesions develop with a time course consistent with a vital role for C22-C24-GalCer in myelin stability. Myelin degeneration and detachment was observed as was abnormal motor behavior originating from a subcortical region. Additional abnormalities included bilateral and symmetrical vacuolization and gliosis in specific brain areas, which corresponded to some extent to the pattern of ceramide synthase 2 expression, with astrogliosis considerably more pronounced than microglial activation. Unexpectedly, unidentified storage materials were detected in lysosomes of astrocytes, reminiscent of the accumulation that occurs in lysosomal storage disorders. Together, our data demonstrate a key role in the brain for SLs containing very long acyl chains and in particular GalCer with a reduction in their levels leading to distinctive morphological abnormalities in defined brain regions.

Fullerene sugar balls

Fullerene hexakis-adducts bearing 12 peripheral carbohydrate moieties have been prepared by grafting sugar derivatives onto the fullerene core through the copper mediated Huisgen 1,3-dipolar cycloaddition of azides and alkynes.

Role of the oligodendroglial cytoskeleton in differentiation and myelination

Oligodendrocytes, the myelin-forming cells of the central nervous system, are in culture characterized by an elaborate process network, terminating in flat membranous sheets that are rich in myelin-specific proteins and lipids, and spirally wrap axons forming a compact insulating layer in vivo. By analogy with other cell types, maintenance and stability of these processes, as well as the formation of the myelin sheath, likely rely on a pronounced cytoskeleton consisting of microtubules and microfilaments. While the specialized process of wrapping and compaction forming the myelin sheath is not well understood, considerably more is known about how cytoskeletal organization is mediated by extracellular and intracellular signals and other interaction partners during oligodendrocyte differentiation and myelination. Here, we review the current state of knowledge on the role of the oligodendrocyte cytoskeleton in differentiation with an emphasis on signal transduction mechanisms and will attempt to draw out implications for its significance in myelination.

Glycosynaptic microdomains controlling tumor cell phenotype through alteration of cell growth, adhesion, and motility

Glycosphingolipids (GSLs) GM3 (NeuAcalpha3Galbeta4Glcbeta1Cer) and GM2 (GalNAcbeta4[NeuAcalpha3]Galbeta4Glcbeta1Cer) inhibit (i) cell growth through inhibition of tyrosine kinase associated with growth factor receptor (GFR), (ii) cell adhesion/motility through inhibition of integrin-dependent signaling via Src kinases, or (iii) both cell growth and motility by blocking "cross-talk" between integrins and GFRs. These inhibitory effects are enhanced when GM3 or GM2 are in complex with specific tetraspanins (TSPs) (CD9, CD81, CD82). Processes (i)-(iii) occur through specific organization of GSLs with key molecules (TSPs, caveolins, GFRs, integrins) in the glycosynaptic microdomain. Some of these processes are shared with epithelial-mesenchymal transition induced by TGFbeta or under hypoxia, particularly that associated with cancer progression.

Polar lipid remodeling and increased sulfatide expression are associated with the glioma therapeutic candidates, wild type p53 elevation and the topoisomerase-1 inhibitor, irinotecan

We report changes in gene and polar lipid expression induced by adenovirus-delivered wild-type (wt) p53 gene and chemotherapy of U87 MG glioblastoma cells, a treatment known to trigger apoptosis and cell cycle arrest. Sulfatides (sulfonated glycolipids) were most highly modulated by wild-type p53 treatment; however, no changes were observed in expression levels of mRNA for genes involved in sulfatide metabolism, indicating post-transcriptional control of sulfatide synthesis. Modulation of the aglycones of GD1 and GM1b was observed in wild-type p53-treated cells. The treatment also leads to an increase in phospholipids such as phosphatidyl inositols, phosphatidyl serines, phosphatidyl glycerols, and phosphatidyl ethanolamines, especially hydroxylated phospholipids. These dramatic changes in the composition of cellular glycolipids in response to p53 gene expression and cytotoxic chemotherapy treatment indicate the large role that they play in cell signaling. The use of the human glioma cell line U87 appears to be an excellent model system both in tissue culture and in intracranial murine xenograft models to further characterize the role of sulfatides in modulating glioma responsivity to therapeutic agents.

[Study of the interactions between oligosaccharides involved in the cell adhesion. Example of the Lewis(x) trisaccharide]

Nature often chooses weak molecular interactions for playing important role in cellular recognition and adhesion. These interactions involve particularly oligosaccharides, which are the structural elements present at the most exterior surface of the cell. Three oligosaccharides were prepared for study of the interaction by vesicle micromanipulation technique. This study allowed us to measure directly, for the first time, a carbohydrate-carbohydrate interaction.

Structural requirements of anti-GD1a antibodies determine their target specificity

The acute motor axonal neuropathy (AMAN) variant of Guillain-Barré syndrome (GBS) is associated with anti-GD1a and anti-GM1 IgG antibodies. The basis of preferential motor nerve injury in this disease is not clear, however, because biochemical studies demonstrate that sensory and motor nerves express similar quantities of GD1a and GM1 gangliosides. To elucidate the pathophysiology of AMAN, we have developed several monoclonal antibodies (mAbs) with GD1a reactivity and reported that one mAb, GD1a-1, preferentially stained motor axons in human and rodent nerves. To understand the basis of this preferential motor axon staining, several derivatives of GD1a were generated by various chemical modifications of N-acetylneuraminic (sialic) acid residues (GD1a NeuAc 1-amide, GD1a NeuAc ethyl ester, GD1a NeuAc 1-alcohol, GD1a NeuAc 1-methyl ester, GD1a NeuAc 7-alcohol, GD1a NeuAc 7-aldehyde) on this ganglioside. Binding of anti-GD1a mAbs and AMAN sera with anti-GD1a Abs to these derivatives was examined. Our results indicate that mAbs with selective motor axon staining had a distinct pattern of reactivity with GD1a-derivatives compared to mAbs that stain both motor and sensory axons. The fine specificity of the anti-GD1a antibodies determines their motor selectivity, which was validated by cloning a new mAb (GD1a-E6) with a chemical and immunocytochemical binding pattern similar to that of GD1a-1 but with two orders of magnitude higher affinity. Control studies indicate that selective binding of mAbs to motor nerves is not due to differences in antibody affinity or ceramide structural specificity. Since GD1a-reactive mAb with preferential motor axon staining showed similar binding to sensory- and motor nerve-derived GD1a in a solid phase assay, we generated computer models of GD1a based on binding patterns of different GD1a-reactive mAbs to different GD1a-derivatives. These modelling studies suggest that critical GD1a epitopes recognized by mAbs are differentially expressed in motor and sensory nerves. The GD1a-derivative binding patterns of AMAN sera resembled those with motor-specific mAbs. On the basis of these findings we postulate that both the fine specificity and ganglioside orientation/exposure in the tissues contribute to target recognition by anti-ganglioside antibodies and this observation provides one explanation for preferential motor axon injury in AMAN.

FA2H is responsible for the formation of 2-hydroxy galactolipids in peripheral nervous system myelin

Myelin in the mammalian nervous system has a high concentration of galactolipids [galactosylceramide (GalCer) and sulfatide] with 2-hydroxy fatty acids. We recently reported that fatty acid 2-hydroxylase (FA2H), encoded by the FA2H gene, is the major fatty acid 2-hydroxylase in the mouse brain. In this report, we show that FA2H also plays a major role in the formation of 2-hydroxy galactolipids in the peripheral nervous system. FA2H mRNA and FA2H activity in the neonatal rat sciatic nerve increased rapidly during developmental myelination. The contents of 2-hydroxy fatty acids were approximately 5% of total galactolipid fatty acids at 4 days of age and increased to 60% in GalCer and to 35% in sulfatides at 60 days of age. The chain length of galactolipid fatty acids also increased significantly during myelination. FA2H expression in cultured rat Schwann cells was highly increased in response to dibutyryl cyclic AMP, which stimulates Schwann cell differentiation and upregulates myelin genes, such as UDP-galactose:ceramide galactosyltransferase and protein zero. These observations indicate that FA2H is a myelination-associated gene. FA2H-directed RNA interference (RNAi) by short-hairpin RNA expression resulted in a reduction of cellular 2-hydroxy fatty acids and 2-hydroxy GalCer in D6P2T Schwannoma cells, providing direct evidence that FA2H-dependent fatty acid 2-hydroxylation is required for the formation of 2-hydroxy galactolipids in peripheral nerve myelin. Interestingly, FA2H-directed RNAi enhanced the migration of D6P2T cells, suggesting that, in addition to their structural role in myelin, 2-hydroxy lipids may greatly influence the migratory properties of Schwann cells.

Structure and function of glycosphingolipids and sphingolipids: recollections and future trends

Based on development of various methodologies for isolation and characterization of glycosphingolipids (GSLs), we have identified a number of GSLs with globo-series or lacto-series structure. Many of them are tumor-associated or developmentally regulated antigens. The major question arose, what are their functions in cells and tissues? Various approaches to answer this question were undertaken. While the method is different for each approach, we have continuously studied GSL or glycosyl epitope interaction with functional membrane components, which include tetraspanins, growth factor receptors, integrins, and signal transducer molecules. Often, GSLs were found to interact with other carbohydrates within a specific membrane microdomain termed "glycosynapse", which mediates cell adhesion with concurrent signal transduction. Future trends in GSL and glycosyl epitope research are considered, including stem cell biology and epithelial-mesenchymal transition (EMT) process.

Weak self-association in a carbohydrate system

The physiological importance of weak interactions between biological macromolecules (molar dissociation constants >10 microM) is now well recognized, particularly with regard to cell adhesion and immunological phenomena, and many weak interactions have been measured for proteins. The concomitant importance of carbohydrate-carbohydrate interactions has also been identified, although no weak interaction between pure carbohydrate systems has ever been measured. We now demonstrate for the first time to our knowledge using a powerful probe for weak interactions--sedimentation velocity in the analytical ultracentrifuge--that at least some carbohydrates (from the class of polysaccharides known as heteroxylans and demonstrated here to be biologically active) can show well-defined weak self-interactions of the "monomer-dimer" type frequently found in protein systems. The weak interaction between the heteroxylans is shown from a temperature dependence study to be likely to be hydrophobic in nature.

Association free energy of dipalmitoylphosphatidylserines in a mixed dipalmitoylphosphatidylcholine membrane

Blood coagulation is strongly dependent on the binding of vitamin K-dependent proteins to cell membranes containing phosphatidylserine (PS) via gamma-carboxyglutamic acid (Gla) domains. The process depends on calcium, which can induce nonideal behavior in membranes through domain formation. Such domain separation mediated by Ca(2+) ions or proteins can have an important contribution to the thermodynamics of the interaction between charged peripheral proteins and oppositely charged membranes. To characterize the properties of lipid-lipid interactions, molecular dynamics, and free energy simulations in a mixed bilayer membrane containing dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine were carried out. The free energy of association between dipalmitoylphosphatidylserines in the environment of dipalmitoylphosphatidylcholines has been calculated by using a novel approach to the dual topology technique of the PS-PC hybrid. Two different methods, free energy perturbation and thermodynamic integration, were used to calculate the free energy difference. In thermodynamic integration runs three schemes were applied to evaluate the integral at the limits of lambda --> 0 or lambda --> 1. Our studies show that the association of two PSs in the environment of PCs is repulsive in the absence of Ca(2+) and becomes favorable in their presence. We also show that the mixed component membrane should exhibit nonideal behavior that will lead to PS clustering.

Interaction of N-linked glycans, having multivalent GlcNAc termini, with GM3 ganglioside

GM3 ganglioside interacts specifically with complex-type N-linked glycans having multivalent GlcNAc termini, as shown for (1) and (2) below. (1) Oligosaccharides (OS) isolated from ConA-non-binding N-linked glycans of ovalbumin, whose structures were identified as penta-antennary complex-type with bisecting GlcNAc, having five or six GlcNAc termini (OS B1, B2), or bi-antennary complex-type having two GlcNAc termini (OS I). OS I is a structure not previously described. (2) Multi-antennary complex-type N-linked OS isolated from fetuin, treated by sialidase followed by beta-galactosidase, having three or four GlcNAc termini exposed. These OS, conjugated to phosphatidylethanolamine (PE), showed clear interaction with (3)H-labeled liposomes containing GM3, when various doses of OS-PE conjugate were adhered by drying to multi-well polystyrene plates. Interaction was clearly observed only with liposomes containing GM3, but not LacCer, Gb4, or GalNAcalpha1-3Gb4 (Forssman antigen). GM3 interaction with PE conjugate of OS B1 or B2 was stronger than that with PE conjugate of OS I. GM3 interacted clearly with PE conjugate of N-linked OS from desialylated and degalactosylated fetuin, but not native fetuin. No binding was observed to cellobiose-PE conjugate, or to OS-PE conjugate lacking GlcNAc terminus. Thus, GM3, but not other GSL liposomes, interacts with various N-linked OS having multiple GlcNAc termini, in general. These findings suggest that the concept of carbohydrate-to-carbohydrate interaction can be extended to interaction of specific types of N-linked glycans with specific GSLs. Natural occurrence of such interaction to define cell biological phenomena is under investigation.

A glycosynapse in myelin?

Myelin, the multilayered membrane which surrounds nerve axons, is the only example of a membranous structure where contact between extracellular surfaces of membrane from the same cell occurs. The two major glycosphingolipids (GSLs) of myelin, galactosylceramide (GalC) and its sulfated form, galactosylceramide I(3)-sulfate (SGC), can interact with each other by trans carbohydrate-carbohydrate interactions across apposed membranes. They occur in detergent-insoluble lipid rafts containing kinases and thus may be located in membrane signaling domains. These signaling domains may contact each other across apposed extracellular membranes, thus forming glycosynapses in myelin. Multivalent forms of these carbohydrates, GalC/SGC-containing liposomes, or galactose conjugated to albumin, have been added to cultured oligodendrocytes (OLs) to mimic interactions which might occur between these signaling domains when OL membranes or the extracellular surfaces of myelin come into contact. These interactions between multivalent carbohydrate and the OL membrane cause co-clustering or redistribution of myelin GSLs, GPI-linked proteins, several transmembrane proteins, and signaling proteins to the same membrane domains. They also cause depolymerization of the cytoskeleton, indicating that they cause transmission of a signal across the membrane. Their effects have similarities to those of anti-GSL antibodies on OLs, shown by others, suggesting that the multivalent carbohydrate interacts with GalC/SGC in the OL membrane. Communication between the myelin sheath and the axon regulates both axonal and myelin function and is necessary to prevent neurodegeneration. Participation of transient GalC and SGC interactions in glycosynapses between the apposed extracellular surfaces of mature compact internodal myelin might allow transmission of signals throughout the myelin sheath and thus facilitate myelin-axonal communication.

Physical Stability of Sonicated Arsonoliposomes: Effect of Calcium Ions

The physical stability of sonicated arsonoliposomes in the absence and presence of Ca(2+) ions is evaluated. Cholesterol-containing arsonoliposomes composed of arsonolipids [having different acyl chains (C(12)-C(18))], or mixtures of arsonolipids with phospholipids (phosphatidylcholine or distearoyl-phosphatidylcholine) were prepared, and physical stability was evaluated in the absence and presence of CaCl(2), by vesicle dispersions turbidity measurements and cryo-electron microscopy morphological assessment. In some cases, vesicle zeta-potential was measured, under identical conditions. Results demonstrate that self-aggregation of the vesicles studied is low and influenced by the acyl chain length of the arsonolipid used, whereas calcium-induced aggregation is higher, correlating well with the decreased values of vesicle zeta-potential in the presence of Ca(2+) ions (weaker electrostatic repulsion). Acyl chain length of arsonolipids used has a significant quantitative effect on Ca(2+)-induced vesicle aggregation mainly for arsonoliposomes that contain phospholipids (mixed), compared with the vesicles that consist of plain arsonolipids (significant effect only for initial aggregation at time 0). Another difference between plain and mixed arsonoliposomes is that for mixed arsonoliposomes Ca(2+)-induced increases in turbidity are irreversible by ethylenediaminotetraacetic acid, suggesting that vesicle fusion is taking place. This was confirmed by cryo-electron microscopy observations. Finally, when phosphatidylcholine is replaced by distearoyl-phosphatidylcholine, arsonoliposomes are more stable in terms of self-aggregation, but in the presence of calcium, the turbidity and morphology results are similar.

Glycoconjugates for the recognition of Bacillus spores

Carbohydrates act as ligands in many biological processes, including the folding and secretion of proteins, cell-cell recognition, adhesion, and sporulation in the Bacillus genus. Fluorescent-labeled disaccharide glycoconjugates have been applied to evaluate binding to bacterial spores assuming that the spore surface is covered with carbohydrates. This study has shown that specific recognition of bacterial spores is based on interactions between disaccharide glycoconjugates acting as ligands and monosaccharide units expressed on the exterior of bacterial spores. Using fluorophore-assisted carbohydrate electrophoresis (FACE), carbohydrates that are expressed on the exterior of the spores were enumerated. The findings have an impact on how to improve ligand selection, essential for sensor development. In addition, the findings provide new information for inhibition of bacterial spores, and in general, demonstrate how carbohydrates function as recognition signals in nature.

Glycosynapses: microdomains controlling carbohydrate-dependent cell adhesion and signaling

The concept of microdomains in plasma membranes was developed over two decades, following observation of polarity of membrane based on clustering of specific membrane components. Microdomains involved in carbohydrate-dependent cell adhesion with concurrent signal transduction that affect cellular phenotype are termed "glycosynapse". Three types of glycosynapse have been distinguished: "type 1" having glycosphingolipid associated with signal transducers (small G-proteins, cSrc, Src family kinases) and proteolipids; "type 2" having O-linked mucin-type glycoprotein associated with Src family kinases; and "type 3" having N-linked integrin receptor complexed with tetraspanin and ganglioside. Different cell types are characterized by presence of specific types of glycosynapse or their combinations, whose adhesion induces signal transduction to either facilitate or inhibit signaling. E.g., signaling through type 3 glycosynapse inhibits cell motility and differentiation. Glycosynapses are distinct from classically-known microdomains termed "caveolae", "caveolar membrane", or more recently "lipid raft", which are not involved in carbohydrate-dependent cell adhesion. Type 1 and type 3 glycosynapses are resistant to cholesterol-binding reagents, whereas structure and function of "caveolar membrane" or "lipid raft" are disrupted by these reagents. Various data indicate a functional role of glycosynapses during differentiation, development, and oncogenic transformation.

Surface Plasmon Resonance Study of Carbohydrate−Carbohydrate Interaction between Various Gangliosides and Gg3-Carrying Polystyrene

Carbohydrate-carbohydrate interactions between Gg3 trisaccharide-carrying polystyrene (PN(Gg3)) and monolayers of several glycosphingolipids (GSLs) were quantitatively investigated by surface plasmon resonance techniques. PN(Gg3) was adsorbed onto a GM3 monolayer strongly and specifically with an apparent affinity constant of K(a) = 2.5 x 10(6) M(-1), and the apparent affinity constants onto GSLs decreased in the following order: GM3 > LacCer > (KDN)GM3 approximately GlcCer > GM2 approximately GD3 approximately GM4 > GM1 approximately 2,6-isoGM3 > ceramide. These results suggest that PN(Gg3) recognizes not only some specified portions of GM3 but also the trisaccharide as a whole. On the other hand, PN(Lac) and PN(Cel) were bound to GSLs less strongly (K(a) approximately 10(4) M(-1)) and less selectively. The kinetic analysis revealed that the selectivity in the adsorption of PN(Gg3) onto the GM3 monolayer is dominated by the faster adsorption rate.

Co-clustering of galactosylceramide and membrane proteins in oligodendrocyte membranes on interaction with polyvalent carbohydrate and prevention by an intact cytoskeleton

We have shown previously that addition of liposomes containing the two major glycosphingolipids of myelin, galactosylceramide (GalC) and cerebroside sulfate (CBS), to cultured oligodendrocytes (OLs) caused clustering of GalC on the extracellular surface and myelin basic protein (MBP) on the cytosolic surface to the same membrane domains. It also caused depolymerization of actin microfilaments and microtubules, indicating that interaction of the liposomes with the OL surface induces transmembrane signal transmission. We show that a multivalent form of galactose conjugated to bovine serum albumin has a similar effect as the multivalent GalC/CBS-containing liposomes. Because GalC and CBS can interact with each other across apposed membranes and because anti-GalC and anti-CBS antibodies also cause redistribution of GalC/CBS and depolymerization of microtubules, we believe that the multivalent carbohydrate interacts with GalC and CBS in the OL membrane. Several myelin-specific transmembrane proteins could be involved in this transmembrane signal transmission from GalC/CBS. We looked at co-clustering of several myelin constituents by confocal microscopy to determine if they are located in or redistribute to GalC/MBP-containing domains. Myelin oligodendrocyte glycoprotein (MOG), proteolipid protein (PLP), MAPK, and some phosphotyrosine-containing proteins were found to co-cluster with GalC and MBP, but myelin-associated glycoprotein (MAG) and phosphatidylinositol-4,5-bisphosphate (PIP(2)) did not. These results suggest that MOG and PLP, but probably not MAG, are possible candidates for transmembrane transmission of the signal received by GalC/CBS. To determine if depolymerization of actin microfilaments was required for co-clustering, or was secondary to clustering, we stabilized F-actin with jasplakinolide. This also prevented depolymerization of the microtubules and prevented clustering of all constituents, including GalC. The prevention of clustering or redistribution of these glycolipids and proteins by an intact cytoskeleton is consistent with the picket fence model.

Intermolecular interactions in dry and rehydrated pure and mixed bilayers of phosphatidylcholine and digalactosyldiacylglycerol: a Fourier transform infrared spectroscopy study

Glycolipids are an important part of almost all biological membranes. Their effects on membrane structure and their interactions with phospholipids, however, have not been extensively studied so far. We have investigated the phase behavior and intermolecular interactions in dry and rehydrated bilayers made from the phospholipid egg phosphatidylcholine (EPC) and the plant chloroplast glycolipid digalactosyldiacylglycerol (DGDG), or from a mixture (1:1) of these lipids, using Fourier transform infrared spectroscopy. We show that there are extensive interactions between EPC and DGDG in mixed membranes, and also between DGDG molecules in pure DGDG membranes, involving sugar OH groups and C[double bond]O, P[double bond]O, and choline moieties in dry membranes. These interactions persist to a certain degree even after rehydration. We present evidence that these interactions influence the mixing behavior in phosphatidylcholine/DGDG membranes and also the phase behavior of both EPC/DGDG and pure DGDG membranes in the dry state.

Glycodendritic structures based on Boltorn hyperbranched polymers and their interactions with Lens culinaris lectin

Multivalent scaffolds bearing carbohydrates have been prepared to mediate biological processes where carbohydrates are involved. These systems consist of dendritic structures based on Boltorn H20 and H30 hyperbranched polymers to which carbohydrates are linked through a convenient spacer. Mannose has been chosen as a sugar unit to test the viability of this strategy. These glycodendritic compounds have been prepared in a few steps with good yields, showing a high solubility in physiological media and low toxicity. The binding of these dendritic polymers to the mannose-binding lectin Lens culinaris (LCA) was studied using STD-NMR experiments and quantitative precipitation assays. The results demonstrate the existence of a clear interaction between the mannose derivative systems and the Lens lectin where the dendritic scaffold does not have an important role in mannose binding but supplies the necessary multivalence for lectin cluster formation. These glycodendritic structures are able to interact with a receptor, and therefore they can be considered as promising tools for biological studies.

Interactions between glucosylceramide and galactosylceramide I(3) sulfate and microstructures formed

The monohexoside glycosphingolipids (GSLs), galactosylceramide (GalC), glucosylceramide (GluC), and their sulfated forms are abundant in cell membranes from a number of tissues. Carbohydrate-carbohydrate interactions between the head groups of some GSLs can occur across apposed membranes and may be involved in cell-cell interactions. In the present study, the ability of GluC to participate in trans interactions with galactosylceramide I(3) sulfate (CBS) was investigated by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy. Gaucher's spleen GluC had polymorphic phase behavior; in its metastable state, it formed large wrinkled vesicles. It transformed to a stable state via an intermediate state in which the surface of the vesicles consisted of narrow ribbons. In the stable state, the narrow ribbons split off from the surface to form membrane fragments and flat and helical ribbons. The strength of the intermolecular hydrogen bonding interactions between the carbonyls increased in the order metastable<intermediate<stable state. Aqueous dispersions of GluC and CBS were combined to allow trans carbohydrate-carbohydrate interaction across apposed bilayers, or the lipids were premixed in a solvent before hydration to allow lateral cis interactions. Premixed dispersions of NFA-GluC and CBS remained in the metastable state even when incubated under stable state conditions. When NFA-GluC dispersions were combined with CBS dispersions, they had a small effect on each other's amide groups in the metastable state. Furthermore, conversion of NFA-GluC to the stable state was inhibited, although it reached the intermediate state, suggesting that some degree of trans interaction between these two lipids occurred.

Effects of calcium-induced aggregation on the physical stability of liposomes containing plant glycolipids

Membranes containing either negatively charged lipids or glycolipids can be aggregated by millimolar concentrations of Ca(2+). In the case of membranes made from the negatively charged phospholipid phosphatidylserine, aggregation leads to vesicle fusion and leakage. However, some glycolipid-containing biological membranes such as plant chloroplast thylakoid membranes naturally occur in an aggregated state. In the present contribution, the effect of Ca(2+)-induced aggregation on membrane stability during freezing and in highly concentrated salt solutions (NaCl+/-CaCl(2)) has been determined in membranes containing different fractions of uncharged galactolipids, or a negatively charged sulfoglucolipid, or the negatively charged phospholipid phosphatidylglycerol (PG), in membranes made from the uncharged phospholipid phosphatidylcholine (PC). In the case of the glycolipids, aggregation did not lead to fusion or leakage even under stress conditions, while it did lead to fusion and leakage in PG-containing liposomes. Liposomes made from a mixture of glycolipids and PG that approximates the lipid composition of thylakoids were very unstable, both during freezing and at high solute concentrations and leakage and fusion were increased in the presence of Ca(2+). Collectively, the data indicate that the effects of Ca(2+)-induced aggregation of liposomes on membrane stability depend critically on the type of lipid involved in aggregation. While liposomes aggregated through glycolipids are highly stable, those aggregated through negatively charged lipids are severely destabilized.

Galactolipids are molecular determinants of myelin development and axo-glial organization

Myelination is a developmentally regulated process whereby myelinating glial cells elaborate large quantities of a specialized plasma membrane that ensheaths axons. The myelin sheath contains an unusual lipid composition in that the glycolipid galactosylceramide (GalC) and its sulfated form sulfatide constitute a large proportion of the total lipid mass. These glycolipids have been implicated in a range of developmental processes such as cell differentiation and myelination initiation, but analyses of mice lacking UDP-galactose:ceramide galactosyltransferase (CGT), the enzyme required for myelin galactolipid synthesis, have more recently demonstrated that the galactolipids more subtly regulate myelin formation. The CGT mutants display a delay in myelin maturation and axo-glial interactions develop abnormally. By interbreeding the CGT mutants with mice that lack myelin-associated glycoprotein, it has been shown that these specialized myelin lipids and proteins act in concert to promote axo-glial adhesion during myelinogenesis. The analysis of the CGT mutants is helping to clarify the roles myelin galactolipids play in regulating the development, and ultimately the function of the myelin sheath.

Complementary Liposomes Based on Phosphatidylcholine: Interaction Effectiveness vs Protective Coating

A prospective targeted drug delivery system was prepared by the introduction of complementary and protective moieties at the external surfaces of liposomes. Thus recognition between hydrogenated phosphatidylcholine-cholesterol-based liposomes was achieved by the interaction of the complementary phosphate and guanidinium groups incorporated in separate liposomes while polyethylene glycol chains (PEG) protected both liposomes from environmental factors. In general, protective coating of liposomes in the range of 5% molar incorporation exerted an inhibitory effect on their recognition but it also permitted effective interaction between complementary liposomes.