Nerve growth factor enhances the expression of the cholinergic-specific ganglioside Chol-1 in cocultures of rat septum and hippocampus

Ganglioside metabolism in a transgenic mouse model of Alzheimer's disease: expression of Chol-1α antigens in the brain

The accumulation of Aβ (amyloid β-protein) is one of the major pathological hallmarks in AD (Alzheimer's disease). Gangliosides, sialic acid-containing glycosphingolipids enriched in the nervous system and frequently used as biomarkers associated with the biochemical pathology of neurological disorders, have been suggested to be involved in the initial aggregation of Aβ. In the present study, we have examined ganglioside metabolism in the brain of a double-Tg (transgenic) mouse model of AD that co-expresses mouse/human chimaeric APP (amyloid precursor protein) with the Swedish mutation and human presenilin-1 with a deletion of exon 9. Although accumulation of Aβ was confirmed in the double-Tg mouse brains and sera, no statistically significant change was detected in the concentration and composition of major ganglio-N-tetraosyl-series gangliosides in the double-Tg brain. Most interestingly, Chol-1α antigens (cholinergic neuron-specific gangliosides), such as GT1aα and GQ1bα, which are minor species in the brain, were found to be increased in the double-Tg mouse brain. We interpret that the occurrence of these gangliosides may represent evidence for generation of cholinergic neurons in the AD brain, as a result of compensatory neurogenesis activated by the presence of Aβ.

Cholinergic-specific glycoconjugates

Cholinergic nerve terminals utilize glycoconjugates in several ways, as surface markers and as structural components of the synaptic vesicles present within them. The surface markers have been discovered immunochemically: antibodies raised against them are able specifically to sensitize the cholinergic subpopulation of mammalian brain synaptosomes to complement-mediated lysis. One such group of antigens (Chol-1) have been identified as a novel series of minor gangliosides having in common a sialylated N-acetylgalactosamine residue. These gangliosides may constitute the major gangliosides at cholinergic terminals. A second surface antigen (Chol-2) is thought to be a protein with an epitope in common with a Torpedo electric organ ganglioside. Cholinergic synaptic vesicles are rich in a proteoglycan which appears to assist in the sequestration of acetylcholine within the vesicle and to stabilize the vesicle membrane during cycles of exocytosis and recovery. It may be the cholinergic equivalent of the chromogranins.

Cholera toxin beta subunit induces the differentiation of human medulloblastoma cell line DEV in a neuronal pathway

Medulloblastomas are primitive neuroectodermal tumours that are thought to arise from multipotent precursor cells in the cerebellum. Medulloblastoma cells may be undifferentiated or exhibit glial, neuronal or ependymal characteristics, suggesting that they may conserve their ability to differentiate in appropriate circumstances. Medulloblastoma cell lines may thus provide models to study the commitment and differentiation of multipotent CNS progenitor cells. A human medulloblastoma cell line, DEV, has previously been shown to differentiate in an astrocytic pathway after infection by the retrovirus HTLV-1. In this study immunofluorescence flow cytometry shows that cholera toxin beta subunit (CT beta), which binds to the ganglioside GM1, induces a twofold increase in the number of DEV cells differentiating towards a neuronal pathway, as shown by the increased proportion and labelling intensity of cells stained by an anti-neurofilament antibody. Immunocytochemistry shows that after 3 days in culture with CT beta, DEV cells develop processes which stain positive for neurofilaments and MAP-1. This suggests that CT beta induces DEV cells to express a more neuronal phenotype.

Distribution of the cholinergic-specific antigen Chol-1 in mouse spinal cord neurons developing in culture

The distribution of the cholinergic-specific ganglioside antigen Chol-1 has been studied by indirect fluorescence immunohistochemistry in mouse spinal cord neurons developing in vitro. Chol-1 is first detected after 9 days of culture where it can be seen in the cell bodies of neurons and in the proximal part of their processes. In cultures of the same age, staining with antisynaptophysin antibody revealed that synapse formation has already taken place and the level of choline acetyltransferase activity was found to have reached a plateau. After 12 days in culture Chol-1 can still be seen in the cytoplasm of certain neurons; however, the anti-Chol-1 staining is now more intense in the region of nerve terminals. Anti-neurofilament staining of cultures at this stage reveals that the neurons are highly differentiated and possess an extensive network of processes. These results show that Chol-1 is expressed late in the development of cholinergic neurons after they have formed synapses; it then appears to be transported to the nerve terminal where it accumulates.

Potassium-induced depolarization displaces exogenously incorporated gangliosides from cortical slices

Freshly diced rat cerebral cortical tissue was incubated with [3H]gangliosides for 30 min, then perfused for 2 h with different physiological solutions. Significantly more labeled (exogenous) gangliosides were displaced when mildly depolarizing concentrations (25 mM) of KCl were included in the perfusion medium. This provides new evidence for an interaction between gangliosides and membrane mechanisms of excitation.