Disruption of GM2/GD2 synthase gene resulted in overt expression of 9-O-acetyl GD3 irrespective of Tis21

Advances in Mass Spectrometry of Gangliosides Expressed in Brain Cancers

Gangliosides are highly abundant in the human brain where they are involved in major biological events. In brain cancers, alterations of ganglioside pattern occur, some of which being correlated with neoplastic transformation, while others with tumor proliferation. Of all techniques, mass spectrometry (MS) has proven to be one of the most effective in gangliosidomics, due to its ability to characterize heterogeneous mixtures and discover species with biomarker value. This review highlights the most significant achievements of MS in the analysis of gangliosides in human brain cancers. The first part presents the latest state of MS development in the discovery of ganglioside markers in primary brain tumors, with a particular emphasis on the ion mobility separation (IMS) MS and its contribution to the elucidation of the gangliosidome associated with aggressive tumors. The second part is focused on MS of gangliosides in brain metastases, highlighting the ability of matrix-assisted laser desorption/ionization (MALDI)-MS, microfluidics-MS and tandem MS to decipher and structurally characterize species involved in the metastatic process. In the end, several conclusions and perspectives are presented, among which the need for development of reliable software and a user-friendly structural database as a search platform in brain tumor diagnostics.

9-O Acetylated Gangliosides in Health and Disease

Glycosphingolipids comprise a lipid class characterized by the presence of sugar moieties attached to a ceramide backbone. The role of glycosphingolipids in pathophysiology has gained relevance in recent years in parallel with the development of analytical technologies. Within this vast family of molecules, gangliosides modified by acetylation represent a minority. Described for the first time in the 1980s, their relation to pathologies has resulted in increased interest in their function in normal and diseased cells. This review presents the state of the art on 9-O acetylated gangliosides and their link to cellular disorders.

Elucidating the Focal Immunomodulatory Clues Influencing Mesenchymal Stem Cells in the Milieu of Intervertebral Disc Degeneration

The intervertebral discs (IVDs) are a relatively mobile joint that interconnects vertebrae of the spine. Intervertebral disc degeneration (IVDD) is one of the leading causes of low back pain, which is most often related to patient morbidity as well as high medical costs. Patients with chronic IVDD often need surgery that may sometimes lead to biomechanical complications as well as augmented degeneration of the adjacent segments. Moreover, treatment modalities like rigid intervertebral fusion, dynamic instrumentation, as well as other surgical interventions are still controversial. Mesenchymal stem cells (MSCs) have exhibited to have immunomodulatory functions and the ability to differentiate into cartilage, making these cells possibly an epitome for IVD regeneration. Transplanted MSCs were able to repair IVDD back to the normal disc milieu via the activation of the generation of extracellular matrix (ECM) proteins such as aggrecan, proteoglycans and collagen types I and II. IVD milieu clues like, periostin, cluster of differentiation, tumor necrosis factor alpha, interleukins, chemokines, transforming growth factor beta, reactive oxygen species, toll-like receptors, tyrosine protein kinase receptor and disialoganglioside, exosomes are capable of influencing the MSCs during treatment of IVDD. ECM microenvironment clues above have potentials as biomarkers as well as accurate molecular targets for therapeutic intervention in IVDD.

The role of gangliosides in the organisation of the node of Ranvier examined in glycosyltransferase transgenic mice

Gangliosides are a family of sialic acid containing glycosphingolipids highly enriched in plasma membranes of the vertebrate nervous system. They are functionally diverse in modulating nervous system integrity, notably at the node of Ranvier, and also act as receptors for many ligands including toxins and autoantibodies. They are synthesised in a stepwise manner by groups of glycosyl- and sialyltransferases in a developmentally and tissue regulated manner. In this review, we summarise and discuss data derived from transgenic mice with different transferase deficiencies that have been used to determine the role of glycolipids in the organisation of the node of Ranvier. Understanding their role at this specialised functional site is crucial to determining differential pathophysiology following directed genetic or autoimmune injury to peripheral nerve nodal or paranodal domains, and revealing the downstream consequences of axo-glial disruption.

A Self-Assembling and Disassembling (SADA) Bispecific Antibody (BsAb) Platform for Curative Two-step Pretargeted Radioimmunotherapy

PURPOSE

Many cancer treatments suffer from dose-limiting toxicities to vital organs due to poor therapeutic indices. To overcome these challenges we developed a novel multimerization platform that rapidly removes tumor-targeting proteins from the blood to substantially improve therapeutic index.

EXPERIMENTAL DESIGN

The platform was designed as a fusion of a self-assembling and disassembling (SADA) domain to a tandem single-chain bispecific antibody (BsAb, anti-ganglioside GD2 × anti-DOTA). SADA-BsAbs were assessed with multiple in vivo tumor models using two-step pretargeted radioimmunotherapy (PRIT) to evaluate tumor uptake, dosimetry, and antitumor responses.

RESULTS

SADA-BsAbs self-assembled into stable tetramers (220 kDa), but could also disassemble into dimers or monomers (55 kDa) that rapidly cleared via renal filtration and substantially reduced immunogenicity in mice. When used with rapidly clearing DOTA-caged PET isotopes, SADA-BsAbs demonstrated accurate tumor localization, dosimetry, and improved imaging contrast by PET/CT. When combined with therapeutic isotopes, two-step SADA-PRIT safely delivered massive doses of alpha-emitting (²²⁵Ac, 1.48 MBq/kg) or beta-emitting (¹⁷⁷Lu, 6,660 MBq/kg) S-2-(4-aminobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid (DOTA) payloads to tumors, ablating them without any short-term or long-term toxicities to the bone marrow, kidneys, or liver.

CONCLUSIONS

The SADA-BsAb platform safely delivered large doses of radioisotopes to tumors and demonstrated no toxicities to the bone marrow, kidneys, or liver. Because of its modularity, SADA-BsAbs can be easily adapted to most tumor antigens, tumor types, or drug delivery approaches to improve therapeutic index and maximize the delivered dose.See related commentary by Capala and Kunos, p. 377.

Gangliosides: The Double-Edge Sword of Neuro-Ectodermal Derived Tumors

Gangliosides, the glycosphingolipids carrying one or several sialic acid residues, are mostly localized at the plasma membrane in lipid raft domains and implicated in many cellular signaling pathways mostly by interacting with tyrosine kinase receptors. Gangliosides are divided into four series according to the number of sialic acid residues, which can be also modified by O-acetylation. Both ganglioside expression and sialic acid modifications can be modified in pathological conditions such as cancer, which can induce either pro-cancerous or anti-cancerous effects. In this review, we summarize the specific functions of gangliosides in neuro-ectodermal derived tumors, and their roles in reprogramming the lipidomic profile of cell membrane occurring with the induction of epithelial-mesenchymal transition.

The ceramide moiety of disialoganglioside (GD3) is essential for GD3 recognition by the sialic acid-binding lectin SIGLEC7 on the cell surface

To analyze the binding specificity of a sialic acid-recognizing lectin, sialic acid-binding Ig-like lectin 7 (SIGLEC7), to disialyl gangliosides (GD3s), here we established GD3-expressing cells by introducing GD3 synthase (GD3S or ST8SIA1) cDNA into a colon cancer cell line, DLD-1, that expresses no ligands for the recombinant protein SIGLEC7-Fc. SIGLEC7-Fc did not recognize newly-expressed GD3 on DLD-1 cells, even though GD3 was highly expressed, as detected by an anti-GD3 antibody. Because milk-derived GD3 could be recognized by this fusion protein when incorporated onto the surface of DLD-1 cells, we compared the ceramides in DLD-1-generated and milk-derived GD3s to identify the SIGLEC7-specific GD3 structures on the cell membrane, revealing that SIGLEC7 recognizes only GD3-containing regular ceramides but not phytoceramides. This was confirmed by knockdown/knockout of the sphingolipid delta(4)-desaturase/C4-monooxygenase (DES2) gene, involved in phytoceramide synthesis, disclosing that DES2 inhibition confers SIGLEC7 binding. Furthermore, knocking out fatty acid 2-hydroxylase also resulted in the emergence of SIGLEC7 binding to the cell surface. To analyze the effects of binding between SIGLEC7 and various GD3 species on natural killer function, we investigated cytotoxicity of peripheral blood mononuclear cells from healthy donors toward GD3S-transfected DLD-1 (DLD-1-GD3S) cells and DLD-1-GD3S cells with modified ceramides. We found that cytotoxicity is suppressed in DLD-1-GD3S cells with dehydroxylated GD3s. These results indicate that the ceramide structures in glycosphingolipids affect SIGLEC7 binding and distribution on the cell surface and influence cell sensitivity to killing by SIGLEC7-expressing effector cells.

The crosstalk between glycosphingolipids and neural stem cells

Until a few years ago, the majority of cell functions were envisioned as the result of protein and DNA activity. The cell membranes were considered as a mere structure of support and/or separation. In the last years, the function of cell membranes has, however, received more attention and their components of lipid nature have also been depicted as important cell mediators and the membrane organization was described as an important determinant for membrane-anchored proteins activity. In particular, because of their high diversity, glycosphingolipids offer a wide possibility of regulation. Specifically, the role of glycosphingolipids, in the fine-tuning of neuron activity, has recently received deep attention. For their pivotal role in vertebrate and mammals neural development, neural stem cells regulation is of main interest especially concerning their further functions in neurological pathology progression and treatment. Glycosphingolipids expression present a developmental regulation. In this view, glycosphingolipids can hold an important role in neural stem cells features because of their heterogeneity and their consequent capacity for eclectic interaction with other cell components.

Gangliosides in Nerve Cell Specification

The central nervous system is generated from progenitor cells that are recognized as neural stem cells (NSCs). NSCs are defined as undifferentiated neural cells that are characterized by the capacity for self-renewal and multipotency. Throughout neural development, NSCs undergo proliferation, migration, and cellular differentiation, and dynamic changes are observed in the composition of carbohydrate-rich molecules, including gangliosides. Gangliosides are sialic acid-containing glycosphingolipids with essential and multifaceted functions in brain development and NSC maintenance, which reflects the complexity of brain development. Our group has pioneered research on the importance of gangliosides for growth factor receptor signaling and epigenetic regulation of ganglioside biosynthesis in NSCs. We found that GD3 is the predominant ganglioside species in NSCs (>80%) and modulates NSC proliferation by interacting with epidermal growth factor receptor signaling. In postnatal brain, GD3 is required for long-term maintenance of NSCs. Deficiency in GD3 leads to developmental and behavioral deficits, such as depression. The synthesis of GD3 is switched to the synthesis of complex, brain-type gangliosides, namely, GM1, GD1a, GD1b, and GT1b, resulting in terminal differentiation and loss of "stemness" of NSCs. In this process, GM1 is augmented by a novel GM1-modulated epigenetic gene regulation mechanism of glycosyltransferases at a later differentiation stage. Consequently, our research suggests that stage-specific gangliosides play specific roles in maintaining NSC activities and in cell fate determination.

High-Affinity GD2-Specific CAR T Cells Induce Fatal Encephalitis in a Preclinical Neuroblastoma Model

The GD2 ganglioside, which is abundant on the surface of neuroblastoma cells, is targeted by an FDA-approved therapeutic monoclonal antibody and is an attractive tumor-associated antigen for cellular immunotherapy. Chimeric antigen receptor (CAR)-modified T cells can have potent antitumor activity in B-cell malignancies, and trials to harness this cytolytic activity toward GD2 in neuroblastoma are under way. In an effort to enhance the antitumor activity of CAR T cells that target GD2, we generated variant CAR constructs predicted to improve the stability and the affinity of the GD2-binding, 14G2a-based, single-chain variable fragment (scFv) of the CAR and compared their properties in vivo We included the E101K mutation of GD2 scFv (GD2-E101K) that has enhanced antitumor activity against a GD2⁺ human neuroblastoma xenograft in vivo However, this enhanced antitumor efficacy in vivo was concomitantly associated with lethal central nervous system (CNS) toxicity comprised of extensive CAR T-cell infiltration and proliferation within the brain and neuronal destruction. The encephalitis was localized to the cerebellum and basal regions of the brain that display low amounts of GD2. Our results highlight the challenges associated with target antigens that exhibit shared expression on critical normal tissues. Despite the success of GD2-specific antibody therapies in the treatment of neuroblastoma, the fatal neurotoxicity of GD2-specific CAR T-cell therapy observed in our studies suggests that GD2 may be a difficult target antigen for CAR T-cell therapy without additional strategies that can control CAR T-cell function within the CNS. Cancer Immunol Res; 6(1); 36-46. ©2017 AACR.

Targeting O-Acetyl-GD2 Ganglioside for Cancer Immunotherapy

Target selection is a key feature in cancer immunotherapy, a promising field in cancer research. In this respect, gangliosides, a broad family of structurally related glycolipids, were suggested as potential targets for cancer immunotherapy based on their higher abundance in tumors when compared with the matched normal tissues. GD2 is the first ganglioside proven to be an effective target antigen for cancer immunotherapy with the regulatory approval of dinutuximab, a chimeric anti-GD2 therapeutic antibody. Although the therapeutic efficacy of anti-GD2 monoclonal antibodies is well documented, neuropathic pain may limit its application. O-Acetyl-GD2, the O-acetylated-derivative of GD2, has recently received attention as novel antigen to target GD2-positive cancers. The present paper examines the role of O-acetyl-GD2 in tumor biology as well as the available preclinical data of anti-O-acetyl-GD2 monoclonal antibodies. A discussion on the relevance of O-acetyl-GD2 in chimeric antigen receptor T cell therapy development is also included.

Exogenous and Endogeneous Disialosyl Ganglioside GD1b Induces Apoptosis of MCF-7 Human Breast Cancer Cells

Gangliosides have been known to play a role in the regulation of apoptosis in cancer cells. This study has employed disialyl-ganglioside GD1b to apoptosis in human breast cancer MCF-7 cells using exogenous treatment of the cells with GD1b and endogenous expression of GD1b in MCF-7 cells. First, apoptosis in MCF-7 cells was observed after treatment of GD1b. Treatment of MCF-7 cells with GD1b reduced cell growth rates in a dose and time dependent manner during GD1b treatment, as determined by XTT assay. Among the various gangliosides, GD1b specifically induced apoptosis of the MCF-7 cells. Flow cytometry and immunofluorescence assays showed that GD1b specifically induces apoptosis in the MCF-7 cells with Annexin V binding for apoptotic actions in early stage and propidium iodide (PI) staining the nucleus of the MCF-7 cells. Treatment of MCF-7 cells with GD1b activated apoptotic molecules such as processed forms of caspase-8, -7 and PARP (Poly(ADP-ribose) polymerase), without any change in the expression of mitochondria-mediated apoptosis molecules such as Bax and Bcl-2. Second, to investigate the effect of endogenously produced GD1b on the regulation of cell function, UDP-gal: β1,3-galactosyltransferase-2 (GD1b synthase, Gal-T2) gene has been transfected into the MCF-7 cells. Using the GD1b synthase-transfectants, apoptosis-related signal proteins linked to phenotype changes were examined. Similar to the exogenous GD1b treatment, the cell growth of the GD1b synthase gene-transfectants was significantly suppressed compared with the vector-transfectant cell lines and transfection activated the apoptotic molecules such as processed forms of caspase-8, -7 and PARP, but not the levels of expression of Bax and Bcl-2. GD1b-induced apoptosis was blocked by caspase inhibitor, Z-VAD. Therefore, taken together, it was concluded that GD1b could play an important role in the regulation of breast cancer apoptosis.

Anti-GD2 mAb and Vorinostat synergize in the treatment of neuroblastoma

Neuroblastoma (NBL) is a childhood malignancy of the sympathetic nervous system. For high-risk NBL patients, the mortality rate is still over 50%, despite intensive multimodal treatment. Anti-GD2 monoclonal antibody (mAB) in combination with systemic cytokine immunotherapy has shown clinical efficacy in high-risk NBL patients. Targeted therapy using histone deacetylase inhibitors (HDACi) is currently being explored in cancer treatment and already shows promising results. Using our recently developed transplantable TH-MYCN NBL model, we here report that the HDAC inhibitor Vorinostat synergizes with anti-GD2 mAb therapy in reducing NBL tumor growth. Further mechanistic studies uncovered multiple mechanisms for the observed synergy, including Vorinostat-induced specific NBL cell death and upregulation of the tumor antigen GD2 on the cell surface of surviving NBL cells. Moreover, Vorinostat created a permissive tumor microenvironment (TME) for tumor-directed mAb therapy by increasing macrophage effector cells expressing high levels of Fc-receptors (FcR) and decreasing the number and function of myeloid-derived suppressor cells (MDSC). Collectively, these data imply further testing of other epigenetic modulators with immunotherapy and provide a strong basis for clinical testing of anti-GD2 plus Vorinostat combination therapy in NBL patients.

Ganglioside accumulation in activated glia in the developing brain: comparison between WT and GalNAcT KO mice

Our previous studies have shown accumulation of GM2 ganglioside during ethanol-induced neurodegeneration in the developing brain, and GM2 elevation has also been reported in other brain injuries and neurodegenerative diseases. Using GM2/GD2 synthase KO mice lacking GM2/GD2 and downstream gangliosides, the current study explored the significance of GM2 elevation in WT mice. Immunohistochemical studies indicated that ethanol-induced acute neurodegeneration in postnatal day 7 (P7) WT mice was associated with GM2 accumulation in the late endosomes/lysosomes of both phagocytic microglia and increased glial fibrillary acidic protein (GFAP)-positive astrocytes. However, in KO mice, although ethanol induced robust neurodegeneration and accumulation of GD3 and GM3 in the late endosomes/lysosomes of phagocytic microglia, it did not increase the number of GFAP-positive astrocytes, and the accumulation of GD3/GM3 in astrocytes was minimal. Not only ethanol, but also DMSO, induced GM2 elevation in activated microglia and astrocytes along with neurodegeneration in P7 WT mice, while lipopolysaccharide, which did not induce significant neurodegeneration, caused GM2 accumulation mainly in lysosomes of activated astrocytes. Thus, GM2 elevation is associated with activation of microglia and astrocytes in the injured developing brain, and GM2, GD2, or other downstream gangliosides may regulate astroglial responses in ethanol-induced neurodegeneration.

A role for Galgt1 in skeletal muscle regeneration

BACKGROUND

Cell surface glycans are known to play vital roles in muscle membrane stability and muscle disease, but to date, roles for glycans in muscle regeneration have been less well understood. Here, we describe a role for complex gangliosides synthesized by the Galgt1 gene in muscle regeneration.

METHODS

Cardiotoxin-injected wild type (WT) and Galgt1 (-/-) muscles, and mdx and Galgt1 (-/-) mdx muscles, were used to study regeneration in response to acute and chronic injury, respectively. Muscle tissue was analyzed at various time points for morphometric measurements and for gene expression changes in satellite cell and muscle differentiation markers by quantitative real-time polymerase chain reaction (qRT-PCR). Primary cell cultures were used to measure growth rate and myotube formation and to identify Galgt1 expression changes after cardiotoxin by fluorescence-activated cell sorting (FACS). Primary cell culture and tissue sections were also used to quantify satellite cell apoptosis.

RESULTS

A query of a microarray data set of cardiotoxin-induced mouse muscle gene expression changes identified Galgt1 as the most upregulated glycosylation gene immediately after muscle injury. This was validated by qRT-PCR as a 23-fold upregulation in Galgt1 expression 1 day after cardiotoxin administration and a 16-fold upregulation in 6-week-old mdx muscles. These changes correlated with increased expression of Galgt1 protein and GM1 ganglioside in mononuclear muscle cells. In the absence of Galgt1, cardiotoxin-induced injury led to significantly reduced myofiber diameters after 14 and 28 days of regeneration. Myofiber diameters were also significantly reduced in Galgt1-deficient mdx mice compared to age-matched mdx controls, and this was coupled with a significant increase in the loss of muscle tissue. Cardiotoxin-injected Galgt1 (-/-) muscles showed reduced gene expression of the satellite cell marker Pax7 and increased expression of myoblast markers MyoD, Myf5, and Myogenin after injury along with a tenfold increase in apoptosis of Pax7-positive muscle cells. Cultured primary Galgt1 (-/-) muscle cells showed a normal growth rate but demonstrated premature fusion into myofibers, resulting in an overall impairment of myofiber formation coupled with a threefold increase in muscle cell apoptosis.

CONCLUSIONS

These experiments demonstrate a role for Galgt1 in skeletal muscle regeneration and suggest that complex gangliosides made by Galgt1 modulate the survival and differentiation of satellite cells.

Mice lacking GD3 synthase display morphological abnormalities in the sciatic nerve and neuronal disturbances during peripheral nerve regeneration

The ganglioside 9-O-acetyl GD3 is overexpressed in peripheral nerves after lesioning, and its expression is correlated with axonal degeneration and regeneration in adult rodents. However, the biological roles of this ganglioside during the regenerative process are unclear. We used mice lacking GD3 synthase (Siat3a KO), an enzyme that converts GM3 to GD3, which can be further converted to 9-O-acetyl GD3. Morphological analyses of longitudinal and transverse sections of the sciatic nerve revealed significant differences in the transverse area and nerve thickness. The number of axons and the levels of myelin basic protein were significantly reduced in adult KO mice compared to wild-type (WT) mice. The G-ratio was increased in KO mice compared to WT mice based on quantification of thin transverse sections stained with toluidine blue. We found that neurite outgrowth was significantly reduced in the absence of GD3. However, addition of exogenous GD3 led to neurite growth after 3 days, similar to that in WT mice. To evaluate fiber regeneration after nerve lesioning, we compared the regenerated distance from the lesion site and found that this distance was one-fourth the length in KO mice compared to WT mice. KO mice in which GD3 was administered showed markedly improved regeneration compared to the control KO mice. In summary, we suggest that 9-O-acetyl GD3 plays biological roles in neuron-glia interactions, facilitating axonal growth and myelination induced by Schwann cells. Moreover, exogenous GD3 can be converted to 9-O-acetyl GD3 in mice lacking GD3 synthase, improving regeneration.

Neuronal expression of GalNAc transferase is sufficient to prevent the age-related neurodegenerative phenotype of complex ganglioside-deficient mice

Gangliosides are widely expressed sialylated glycosphingolipids with multifunctional properties in different cell types and organs. In the nervous system, they are highly enriched in both glial and neuronal membranes. Mice lacking complex gangliosides attributable to targeted ablation of the B4galnt1 gene that encodes β-1,4-N-acetylegalactosaminyltransferase 1 (GalNAc-transferase; GalNAcT(-/-)) develop normally before exhibiting an age-dependent neurodegenerative phenotype characterized by marked behavioral abnormalities, central and peripheral axonal degeneration, reduced myelin volume, and loss of axo-glial junction integrity. The cell biological substrates underlying this neurodegeneration and the relative contribution of either glial or neuronal gangliosides to the process are unknown. To address this, we generated neuron-specific and glial-specific GalNAcT rescue mice crossed on the global GalNAcT(-/-) background [GalNAcT(-/-)-Tg(neuronal) and GalNAcT(-/-)-Tg(glial)] and analyzed their behavioral, morphological, and electrophysiological phenotype. Complex gangliosides, as assessed by thin-layer chromatography, mass spectrometry, GalNAcT enzyme activity, and anti-ganglioside antibody (AgAb) immunohistology, were restored in both neuronal and glial GalNAcT rescue mice. Behaviorally, GalNAcT(-/-)-Tg(neuronal) retained a normal "wild-type" (WT) phenotype throughout life, whereas GalNAcT(-/-)-Tg(glial) resembled GalNAcT(-/-) mice, exhibiting progressive tremor, weakness, and ataxia with aging. Quantitative electron microscopy demonstrated that GalNAcT(-/-) and GalNAcT(-/-)-Tg(glial) nerves had significantly increased rates of axon degeneration and reduced myelin volume, whereas GalNAcT(-/-)-Tg(neuronal) and WT appeared normal. The increased invasion of the paranode with juxtaparanodal Kv1.1, characteristically seen in GalNAcT(-/-) and attributed to a breakdown of the axo-glial junction, was normalized in GalNAcT(-/-)-Tg(neuronal) but remained present in GalNAcT(-/-)-Tg(glial) mice. These results indicate that neuronal rather than glial gangliosides are critical to the age-related maintenance of nervous system integrity.

Structural analysis of brain ganglioside acetylation patterns in mice with altered ganglioside biosynthesis

Gangliosides are sialylated membrane glycosphingolipids especially abundant in mammalian brain tissue. Sialic acid O-acetylation is one of the most common structural modifications of gangliosides which considerably influences their chemical properties. In this study, gangliosides extracted from brain tissue of mice with altered ganglioside biosynthesis (St8sia1 null and B4galnt1 null mice) were structurally characterized and their acetylation pattern was analyzed. Extracted native and alkali-treated gangliosides were resolved by high performance thin layer chromatography. Ganglioside mixtures as well as separated individual ganglioside fractions were further analyzed by tandem mass spectrometry. Several O-acetylated brain ganglioside species were found in knockout mice, not present in the wild-type mice. To the best of our knowledge this is the first report on the presence of O-acetylated GD1a in St8sia1 null mice and O-acetylated GM3 species in B4galnt1 null mice. In addition, much higher diversity of abnormally accumulated brain ganglioside species regarding the structure of ceramide portion was observed in knockout versus wild-type mice. Obtained findings indicate that the diversity of brain ganglioside structures as well as acetylation patterns in mice with altered ganglioside biosynthesis, is even higher than previously reported. Further investigation is needed in order to explore the effects of acetylation on ganglioside interactions with other molecules and consequently the physiological role of acetylated ganglioside species.

Profiling and sequence analysis of gangliosides in human astrocytoma by high-resolution mass spectrometry

In this preliminary investigation, a low-grade astrocytoma (AcT) is investigated by high-resolution (HR) mass spectrometry (MS) aiming at characterization of gangliosides with potential biomarker value. The research was conducted towards a comparative mapping of ganglioside expression in AcT, its surrounding tissue (ST) and a normal control brain tissue (NT). HR MS was conducted in the negative ion mode nanoelectrospray ionization (nanoESI). Fragmentation analysis was carried out by collision-induced dissociation (CID) MS(2)-MS(4.) Due to the high resolving power and mass accuracy, by comparative mapping of the ganglioside extracts from AcT, ST and NT, under identical conditions, 37 different species in AcT, 40 in ST and 56 in NT were identified. AcT and ST were found to contain 18 identical ganglioside components. Among all three specimens, ST extract presented the highest levels of sialylation, fucosylation and acetylation, a feature which might be correlated to the tumor expansion in the adjacent brain area. MS mapping indicated also that AcT, ST and NT share one doubly deprotonated molecule at m/z 1063.31, attributable to GT1(d18:1/18:0) or GT1(d18:0/18:1). CID MS(2)-MS(4) on these particular ions detected in AcT and ST provided data supporting GT1c isomer in the investigated astrocytoma tissue. Our results show that HR MS has a remarkable potential in brain cancer research for the determination of tumor-associated markers and for their structural determination.

Functional roles of gangliosides in neurodevelopment: an overview of recent advances

Gangliosides are sialic acid-containing glycosphingolipids that are most abundant in the nervous system. They are localized primarily in the outer leaflets of plasma membranes and participated in cell-cell recognition, adhesion, and signal transduction and are integral components of cell surface microdomains or lipid rafts along with proteins, sphingomyelin and cholesterol. Ganglioside-rich lipid rafts play an important role in signaling events affecting neural development and the pathogenesis of certain diseases. Disruption of gangloside synthase genes in mice induces developmental defects and neural degeneration. Targeting ganglioside metabolism may represent a novel therapeutic strategy for intervention in certain diseases. In this review, we focus on recent advances on metabolic and functional studies of gangliosides in normal brain development and in certain neurological disorders.

Functions and Biosynthesis of O-Acetylated Sialic Acids

Sialic acids have a pivotal functional impact in many biological interactions such as virus attachment, cellular adhesion, regulation of proliferation, and apoptosis. A common modification of sialic acids is O-acetylation. O-Acetylated sialic acids occur in bacteria and parasites and are also receptor determinants for a number of viruses. Moreover, they have important functions in embryogenesis, development, and immunological processes. O-Acetylated sialic acids represent cancer markers, as shown for acute lymphoblastic leukemia, and they are known to play significant roles in the regulation of ganglioside-mediated apoptosis. Expression of O-acetylated sialoglycans is regulated by sialic acid-specific O-acetyltransferases and O-acetylesterases. Recent developments in the identification of the enigmatic sialic acid-specific O-acetyltransferase are discussed.