Résumé des résultats (Abstract)
(Anglais)
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This project was designed to assess the role of apolipoprotein E in the neuronal pathology of Alzheimers Disease (AD). Our role was to use our expertise in the culture of hippocampal neurons, which are particularly susceptible to the disease process, and in dynamic imaging of the neuronal cytoskeleton and particularly the tau microtubule protein which forms abnormal deposits - neurofibrillary tangles - which are one of major neuropathological changes that characterize AD. We had two specific objectives: 1) to provide hippocampal neurons grown in cell culture for analysis to other members of the international team; 2) to perform dynamic imaging studies in living cells using tau protein labelled with green fluorescent protein (tau-GFP) to assess mechanisms potentially involved in regulating tau binding to microtubules that may provide an insight into its abnormal distribution during the disease process. In the first part of this study cells were provided to Dr. Manfred Hüttinger (Institute of Medical Chemistry, Vienna) for analysis of the novel brain-specific low density lipoprotein receptor LR7/8B together with antibodies against the dendrite-specific microtubule-associated protein MAP2. This showed that in neurons LR7/8B is localized in the cell body and proximal dendrites where it may be involved in the clearance of alpha2-macroglobin/proteinase (alpha-M.proteinase) complexes from the surfaces of neurons. These results are interesting in that LR7/8B binds apoE and that alpha-M has been found in neuritic plaques of AD brain suggesting a possible link between the function of this receptor and the disease process (1). In the second aspect of this study Dr. S. Lovestone (Institute of Psychiatry, London) visited our laboratory and performed joint experiments with Dr. S. Kaech on the dynamics of tau protein in live, transfected cells. These experiments were based on the effects of glycogen synthase kinase-3 (GSK-3) on tau protein, which is to phosphorylate it and lower its affinity for microtubules so that it becomes diffusely distributed in the cell. Our results show that, in live transfected cells, this is accompanied by loss of the microtubule bundles that tau normally induces and which represent the normal distribution of microtubules in neurons. We found that when cells expressing both tau-GFP and (GSK-3) are treated with lithium at concentrations within the therapeutic range for depressive disease, GSK-3 phosphorylation of tau is inhibited tau binding to microtubules is restored. This suggests that tau phosphorylation and binding to microtubules is altered in brain neurons of patients undergoing lithium therapy. Furthermore since the abnormal paired helical filaments of AD brain contain tau which is highly phosphorylated at GSK-3 dependent phosphorylation sites raises the possiblity that lithium treatment could influence the disease process (2).
References
1. Stockinger, W., Hengstschlager-Ottnad, E., Novak, S., Matus, A., M, H., Bauer, J., Lassmann, H., Schneider, W. J., and Nimpf, J. (1998) J Biol Chem 273(48), 32213-21
2. Lovestone, S., Davis, D. R., Webster, M.-T., Kaech, S., Brion, J.-P., Matus, A., and Anderton, B. H. (1999) Biol. Psychiatry 45(8), 995-1003
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