Gangliosides and neuronal-astrocytic interactions

Analysis of human hippocampus gangliosides by fully-automated chip-based nanoelectrospray tandem mass spectrometry

Modern microfluidic devices are currently introduced in electrospray (ESI) mass spectrometry (MS), tending to substitute the classical capillary-based ESI infusion. Automated systems using the combination of robotized sample handling and chip-based ESI are significantly increasing the analysis reproducibility, precision, throughput, and efficiency. In the last couple of years our group developed the chip-based ESI-MS approach for glycomics in biomedical research and applied it for oligosaccharide, glycopeptide and ganglioside investigation. Here we report upon the optimization and application of this modern technique for the analysis of differential ganglioside expression patterns in human fetal and adult hippocampus. By this methodology, ganglioside species exhibiting high degree of heterogeneity in the ceramide motifs and biologically-relevant modifications could be identified in human hippocampus. The ultra-high reproducibility of the experiments uniquely provided by the chip-ESI approach allowed for a reliable MS-based ganglioside comparative assay. Moreover, the particular feature of chip ESI-tandem MS to provide structural information at high sensitivity was useful for detailed characterization of hippocampus-associated species. The experimental data presented in this study indicate the benefits of microfluidic/MS for determination of the topospecific brain ganglioside composition and development-related changes in their expression, which might be of high value in clinical investigation and for studies related to ganglioside-based therapy of central nervous system diseases.

Anencephaly: structural characterization of gangliosides in defined brain regions

Gangliosides from histopathologically-defined human cerebrum-resembling remnant and cerebellum from 37 and 30 gestational week-old anencephaluses were identified using mass spectrometry and high performance thin layer chromatography combined with immunochemical analysis in comparison to respective normal newborn/fetal and adult brain regions. A novel strategy of nano-electrospray ionization quadrupole time-of-flight tandem MS has been developed for identification of ganglioside components in complex mixtures. By morphoanatomical and histological investigation the anencephalic cerebral remnant was found to be aberrant, while the anencephalic cerebellum was defined as normal. Total ganglioside concentrations in the anencephalic cerebral remnant and the cerebellum were 34% and 13% lower in relation to the age-matched controls. In the cerebral remnant, GD3, GM2 and GT1b were elevated, while GD1a was decreased in the anencephalic cerebral remnant, but enriched in anencephalic cerebellum. GQ1b was reduced in both anencephalic regions. Gg4Cer, GM1b and GD1alpha, members of the alpha-series biosynthetic pathway, and neolacto-series gangliosides were found to be present in anencephalic, as well as in normal, fetal and adult brain tissues, indicating the occurrence of these biosynthetic pathways in human brain. In both cerebral and cerebellar anencephalic tissues, GM1b, GD1alpha, nLM1 and nLD1 were expressed at a higher rate in relation to normal tissue. It can be demonstrated that the anencephalic cerebral remnant, as a primitive brain structure, represents a naturally-occurring model to study the ganglioside involvement in induction of aberrant brain development.

Nano-electrospray ionization time-of-flight mass spectrometry of gangliosides from human brain tissue

A general approach for the detection and structural elucidation of brain ganglioside species GM1, GD1 and GT1 by nano-electrospray ionization quadrupole time-of-flight (nanoESI-QTOF) mass spectrometry (MS), using combined data from MS and MS/MS analysis of isolated native ganglioside fractions in negative ion mode and their permethylated counterparts in the positive ion mode is presented. This approach was designed to detect and sequence gangliosides present in preparatively isolated ganglioside fractions from pathological brain samples available in only very limited amounts. In these fractions mixtures of homologue and isobaric structures are present, depending on the ceramide composition and the position of the sialic acid attachment site. The interpretation of data for the entire sequence, derived from A, B, C and Y ions by nanoESI-QTOFMS/MS in the negative ion mode of native fractions, can be compromised by ions arising from double and triple internal cleavages. To distinguish between isobaric carbohydrate structures in gangliosides, such as monosialogangliosides GM1a and GM1b, disialogangliosides GD1a, GD1b and GD1c or trisialogangliosides GT1b, GT1c and GT1d, the samples were analysed after permethylation in the positive ion nanoESI-QTOFMS/MS mode, providing set of data, which allows a clear distinction for assignment of outer and inner fragment ions according to their m/z values. The fragmentation patterns from native gangliosides obtained by low-energy collision induced dissociation (CID) by nanoESI-QTOF show common behaviour and follow inherent rules. The combined set of data from the negative and positive ion mode low-energy CID can serve for the detection of structural isomers in mixtures, and to trace new, not previously detected, components.

Neurite outgrowth inhibitors in gliotic tissue

Gliotic tissue is the major obstacle to axon regeneration after CNS injury. We designed tissue culture assays to search for molecules responsible for neurite outgrowth inhibition in gliotic tissue. All the inhibitory activity in injured brain tissue was located in a plasma membrane heparan-sulphate and condroitin-sulphate type-proteoglycan of apparent molecular weight 200 kDalton. The proteoglycan core protein (apparent MW 48,000 kD) was biologically inactive, whereas the glycosamine-glycan (GAG) chains accounted for the inhibitory activity. Because of its cell location and mode of induction, the inhibitor was called injured membrane proteoglycan, IMP. IMP prevented neurite outgrowth initiation when attached to the culture substrate and caused growth cone collapse when added in solution to neurons with already growing neurites. We concluded that IMP was responsible for preventing injured CNS fibre regeneration. Double-staining immunohistochemistry of normal and gliotic tissue with anti-IMP monoclonal antibodies together with glial and neuronal markers, permitted the unequivocal definition of inhibitor presenting cells by confocal microscopy. IMP-immunostaining in normal CNS was observed exclusively on neurons. However, after a lesion, immunostaining occurred primarily on intensely GFAP-positive reactive astrocytes, but not on OX-42 positive microglia. The availability of antibodies permitted rapid affinity-purification of the neurite inhibitor and comparison with similar molecules possibly expressed during development. IMP itself or a highly related form, was expressed in embryonic brain, reaching maximal expression around postnatal day 3 and decreasing strongly in normal adult tissue. Perinatal rat brain proteoglycans inhibited neurite outgrowth similarly, though not identically, to IMP. Our data suggest that perinatal membrane and injured membrane proteoglycans may differ in GAG composition. IMP-like immunoreactivity was also found in developing brain, predominantly in neurons in normal brain, associating after a lesion with reactive astrocytes. Thes results suggest that injury evokes re-expression of IMP previously expressed during CNS development. One of the monoclonal antibodies to IMP blocked inhibitory activity, restoring neurite outgrowth in vitro. We are currently preparing Fab fragments to test the possibility that the antibody may block inhibition of central sprout growth in vivo. The combined use of blocking antibody fragments to neurite outgrowth inhibitors and transplants of growth-promoting glia, may help in the repair brain and spinal cord lesions.