Human Cerebellum Gangliosides: A Comprehensive Analysis by Ion Mobility Tandem Mass Spectrometry

The human cerebellum is an ultraspecialized region of the brain responsible for cognitive functions and movement coordination. The fine mechanisms through which the process of aging impacts such functions are not well understood; therefore, a rigorous exploration of this brain region at the molecular level is deemed necessary. Gangliosides, sialylated glycosphingolipids, highly and specifically expressed in the human central nervous system, represent possible molecular markers of cerebellum development and aging. In this context, for a comprehensive determination of development- and age-specific components, we have conducted here a comparative profiling and structural determination of the gangliosides expressed in fetal cerebellum in two intrauterine developmental stages and aged cerebellum by ion mobility separation (IMS) mass spectrometry (MS) and tandem MS (MS/MS). Due to the high sensitivity and efficiency of separation provided by IMS MS, no less than 551 chemically distinct species were identified, which represents 4.5 times more gangliosides than ever discovered in this brain region. The detailed assessment of fetal vs aged cerebellum gangliosidome showed marked discrepancies not only in the general number of the species expressed, but also in their sialylation patterns, the modifications of the glycan core, and the composition of the ceramides. All of these characteristics are potential markers of cerebellum development and aging. The structural analysis by collision-induced dissociation (CID) documented the occurrence of GD1b (d18:1/18:0) isomer in the fetal cerebellum in the second gestational trimester, with all probability of GQ1b (t18:1/18:0) in the near-term fetus and of GQ1b (d18:1/18:0) in aged cerebellum.

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.

Plasma Membrane Calcium ATPase-Neuroplastin Complexes Are Selectively Stabilized in GM1-Containing Lipid Rafts

The recent identification of plasma membrane (Ca²⁺)-ATPase (PMCA)-Neuroplastin (Np) complexes has renewed attention on cell regulation of cytosolic calcium extrusion, which is of particular relevance in neurons. Here, we tested the hypothesis that PMCA-Neuroplastin complexes exist in specific ganglioside-containing rafts, which could affect calcium homeostasis. We analyzed the abundance of all four PMCA paralogs (PMCA1-4) and Neuroplastin isoforms (Np65 and Np55) in lipid rafts and bulk membrane fractions from GM2/GD2 synthase-deficient mouse brains. In these fractions, we found altered distribution of Np65/Np55 and selected PMCA isoforms, namely PMCA1 and 2. Cell surface staining and confocal microscopy identified GM1 as the main complex ganglioside co-localizing with Neuroplastin in cultured hippocampal neurons. Furthermore, blocking GM1 with a specific antibody resulted in delayed calcium restoration of electrically evoked calcium transients in the soma of hippocampal neurons. The content and composition of all ganglioside species were unchanged in Neuroplastin-deficient mouse brains. Therefore, we conclude that altered composition or disorganization of ganglioside-containing rafts results in changed regulation of calcium signals in neurons. We propose that GM1 could be a key sphingolipid for ensuring proper location of the PMCA-Neuroplastin complexes into rafts in order to participate in the regulation of neuronal calcium homeostasis.

Ganglioside Composition Distinguishes Anaplastic Ganglioglioma Tumor Tissue from Peritumoral Brain Tissue: Complementary Mass Spectrometry and Thin-Layer Chromatography Evidence

Gangliosides serve as antitumor therapy targets and aberrations in their composition strongly correlate with tumor growth and invasiveness. Anaplastic ganglioglioma is a rare, poorly characterized, malignant neuronal–glial tumor type. We present the first comparative characterization of ganglioside composition in anaplastic ganglioglioma vs. peritumoral and healthy brain tissues by combining mass spectrometry and thin-layer chromatography. Anaplastic ganglioglioma ganglioside composition was highly distinguishable from both peritumoral and healthy tissue despite having five to six times lower total content. Ten out of twelve MS-identified ganglioside classes, defined by unique glycan residues, were represented by a large number and considerable abundance of individual species with different fatty acid residues (C16–C24) in ceramide portions. The major structurally identified class was tumor-associated GD3 (>50%) with 11 species; GD3 (d18:1/24:0) being the most abundant. The dominant sphingoid base residue in ganglioside ceramides was sphingosine (d18:1), followed by eicosasphingosine (d20:1). The peritumoral tissue ganglioside composition was estimated as normal. Specific ganglioside composition and large variability of ganglioside ceramide structures determined in anaplastic ganglioglioma demonstrate realistic ganglioside expression patterns and correspond to the profile of high-grade malignancy brain tumors.

Gangliosides of Human Glioblastoma Multiforme: A Comprehensive Mapping and Structural Analysis by Ion Mobility Tandem Mass Spectrometry

Glioblastoma multiforme (GBM), a malignant, highly aggressive, grade IV brain tumor, which rapidly infiltrates into the nearby tissue, has drawn a significant amount of attention because of its poor prognosis and the limited treatment options available. In GBM, nearly all tumor cells exhibit aberrant cell-surface glycosylation patterns due to the alteration of their biosynthesis or postsynthesis modification process. Since gangliosides (GGs) are acknowledged as tumor-associated antigens, we have carried out here a comprehensive profiling of native ganglioside mixtures extracted and purified from GBM specimens. For this purpose, high performance ion mobility separation mass spectrometry (IMS MS) was thoroughly optimized to allow the discovery of GBM-specific structures and the assessment of their roles as tumor markers or possible associated antigens. GG separation by IMS according to the charge state, carbohydrate chain length, degree of sialylation, and ceramide composition led to the identification of no less than 160 distinct components, which represents 3-fold the number of structures identified before. The detected GGs and asialo-GGs were found characterized by a high heterogeneity in their ceramide and glycan compositions, encompassing up five Neu5Ac residues. The tumor was found dominated in equal and high proportions by GD3 and GT1 forms, with a particular incidence of C24:1 fatty acids in the ceramide. By the occurrence of only one mobility feature and the diagnostic fragment ions, the IMS tandem MS conducted using collision-induced dissociation (CID) disclosed for the first time the presence of GT1c(d18:1/24:1) newly proposed here as a potential GBM marker.

High resolution mass spectrometry provides novel insights into the ganglioside pattern of brain cavernous hemangioma

In this study we have optimized nanoelectrospray ionization (nanoESI) high resolution mass spectrometry (HR MS) performed on Orbitrap instrument in the negative ion mode for the determination of the composition and structure of gangliosides extracted from human brain cavernous hemangioma. The optimized HR MS platform, allowed the discrimination of 62 ions, corresponding to 52 different ganglioside species, which represents roughly twice the number of species existing in the current inventory of human brain hemangioma-associated gangliosides. The experiments revealed a ganglioside pattern dominated by GD-type of structures as well as an elevated incidence of species characterized by a low degree of sialylation and short glycan chains, including asialo GA1 (d18:1/18:0), which offer a new perspective upon the ganglioside composition in this benign tumor. Many of the structures are characteristic for this type of tumor only and are to be considered in further investigations for their potential use in early brain hemangioma diagnosis based on molecular markers. The detailed fragmentation analysis performed by collision-induced dissociation (CID) tandem MS provided information of structural elements related to the glycan core and ceramide moiety, which confirmed the molecular configuration of GD3 (d18:1/24:1) and GD3 (d18:1/24:2) species with potential biomarker role.

Orbitrap mass spectrometry for monitoring the ganglioside pattern in human cerebellum development and aging

We have developed here a superior approach based on high-resolution (HR) mass spectrometry (MS) for monitoring the changes occurring with development and aging in the composition and structure of cerebellar gangliosidome. The experiments were focused on the comparative screening and structural analysis of gangliosides expressed in fetal and aged cerebellum by Orbitrap MS with nanoelectrospray ionization (nanoESI) in the negative ion mode. The employed ultrahigh-resolution MS platform allowed the discrimination, without the need of previous separation, of 159 ions corresponding to 120 distinct species in the native ganglioside mixtures from fetal and aged cerebellar biopsies, many more than detected before, when MS platforms of lower resolution were employed. A number of gangliosides, in particular polysialylated belonging to GT, GQ, GP, and GS classes, modified by O-fucosylation, O-acetylation, or CH₃ COO^- were discovered here, for the first time in human cerebellum. These components, found differently expressed in fetal and aged tissues, indicated that the ganglioside profile in cerebellum is development stage- and age-specific. Following the fragmentation analysis by high-energy collision-induced dissociation (HCD) tandem MS (MS/MS), we have also observed that the intimate structure of certain compounds has not changed during the development and aging of the brain, an aspect which could open new directions in the investigation of ganglioside biomarkers in cerebellar tissue.

Gangliosidome of human anencephaly: A high resolution multistage mass spectrometry study

Widely dispersed throughout the entire body tissues, gangliosides (GGs) are essential components of neuronal cell membranes, where exhibit a vital role in neuronal function and brain development, directly influencing the neural tube formation, neurogenesis, neurotransmission, etc. Due to several factors, partial or complete closing faults of the fetal neural tube may occur in the first trimester of pregnancy, generating a series of neural tube defects (NTD), among which anencephaly. The absence in anencephaly of the forebrain and skull bones determines the exposure to the amniotic fluid of the remaining brain tissue and the spinal cord, causing the degeneration of the nervous system tissue. Based on the previously achieved information related to the direct alteration of neural development with deficient concentration of several GGs, a systematic and comparative mass spectrometry (MS) mapping assay on GGs originating from fetuses in different intrauterine developmental stages, i.e. the 29th (denoted An29), 35th (An35) and the 37th (An37) gestational weeks was here conducted. Our approach, based on Orbitrap MS under high sensitivity, resolution and mass accuracy conditions, enabled for the first time the nanoelectrospray ionization, detection and identification of over 150 glycoforms, mainly novel, polysialylated species. Such a pattern, specific for incipient developmental stages reliably documents the brain development stagnation, characteristic for anencephaly. Further, the fragmentation MS²-MS³ experiments by collision induced dissociation (CID) confirmed the incidence in all three samples of GT2(d18:1/16:2) as a potential biomarker. Therefore, this fingerprinting of the anencephalic gangliosidome may serve in development of approaches for routine screening and early diagnosis.

Ion mobility mass spectrometry provides novel insights into the expression and structure of gangliosides in the normal adult human hippocampus

General work-flow for ganglioside analysis by IM-MS.

Electrospray Ionization Ion Mobility Mass Spectrometry of Human Brain Gangliosides

The progress of ion mobility spectrometry (IMS), together with its association to mass spectrometry (MS), opened new directions for the identification of various metabolites in complex biological matrices. However, glycolipidomics of the human brain by IMS MS represents an area untouched up to now, because of the difficulties encountered in brain sampling, analyte extraction, and IMS MS method optimization. In this study, IMS MS was introduced in human brain ganglioside (GG) research. The efficiency of the method in clinical glycolipidomics was demonstrated on a highly complex mixture extracted from a normal fetal frontal lobe (FL37). Using this approach, a remarkably rich molecular ion pattern was discovered, which proved the presence of a large number of glycoforms and an unpredicted diversity of the ceramide chains. Moreover, the results showed for the first time the occurrence of GGs in the human brain with a much higher degree of sialylation than previously reported. Using IMS MS, the entire series starting from mono- up to octasialylated GGs was detected in FL37. These findings substantiate early clinical reports on the direct correlation between GG sialylation degree and brain developmental stage. Using IMS CID MS/MS, applied here for the first time to gangliosides, a novel, tetrasialylated O-GalNAc modified species with a potential biomarker role in brain development was structurally characterized. Under variable collision energy, a high number of sequence ions was generated for the investigated GalNAc-GQ1(d18:1/18:0) species. Several fragment ions documented the presence of the tetrasialo element attached to the inner Gal, indicating that GalNAc-GQ1(d18:1/18:0) belongs to the d series.

Database and data analysis application for structural characterization of gangliosides and sulfated glycosphingolipids by negative ion mass spectrometry

Gangliosides and sulfated glycosphingolipids, as building and functional components of animal cell membranes, participate in cell-to-cell interactions and signaling, but also in changes of cell architecture due to different pathophysiological events. In order to enable higher throughput and to facilitate structural characterization of gangliosides/sulfo-glycosphingolipids (GSL) and their neutral GSL counterparts by negative ion mass spectrometry (MS) and tandem MS techniques, a database and data analysis application have been developed. In silico developed glycosphingolipid database considers a high diversity of ceramide compositions, several sialic acid types (N-acetylneuraminic acid, N-glycolylneuraminic acid and 2-keto-3-deoxynononic acid) as well as possible additional substitutions/modifications of glycosphingolipids, such as O-acetylation, de-N-acetylation, fucosylation, glucuronosylation, sulfation, attachment of repeating terminal hexose-N-acetylhexosamine- (Hex-HexNAc-)1-6 extension, and possible lactone forms. Data analysis application, named GSL-finder, enables correlation of negative ion MS and/or low-energy tandem MS spectra with the database structures. The GSL-database construction and the GSL-finder application searching rules are explained. Validation conducted on GD1a fraction as well as on complex mixtures of native gangliosides isolated from different mammalian brain tissues (human fetal and adult brain, and calf brain tissue) demonstrated agreement with previous studies. Plain, fast, and automated routine for structural characterization of gangliosides/sulfated glycosphingolipids and their neutral GSL counterparts described here could facilitate and improve mass spectrometric analysis of complex glycosphingolipid mixtures originating from variety of normal and pathological biomaterial, where it is known that distinctive changes in glycosphingolipid composition occur.

Mass Spectrometry of Gangliosides from Human Sensory and Motor Cortex

Sialylated glycosphingolipids, known as gangliosides, are highly expressed in the central nervous system exhibiting region-specific composition in correlation to the specialised functions of particular brain regions. In the present study high resolution tandem mass spectrometry on a quadrupole time-of-flight instrument with nanoelectrospray was optimised and applied for the first comparative assessment of the ganglioside profile in single specimens of adult human motor and somatosensory cortex. In the second stage, the structural analysis performed by collision induced dissociation tandem MS disclosed the presence in motor cortex of a fucose-ganglioside Fuc-GM1 (d18 : 1/20 : 0) isomer exhibiting both N-acetylneuraminic acid and fucose residues linked to the inner galactose.