The formation of tau pathological phospho-epitopes in the axon is prevented by the dephosphorylation of selective sites in primary hippocampal neurons over-expressing human tau

Département de Pathologie et Biologie Cellulaire, Université de Montréal, Montréal, Québec, Canada.
Journal of Neurochemistry (Impact Factor: 4.28). 09/2010; 114(5):1353-67. DOI: 10.1111/j.1471-4159.2010.06855.x
Source: PubMed


J. Neurochem. (2010) 114, 1353–1367.
In tauopathies including Alzheimer’s disease, the axonal microtubule-associated protein tau becomes hyperphosphorylated at pathological epitopes and accumulates in the somato-dendritic compartment. However, it remains unclear whether tau becomes phosphorylated at these epitopes in the somato-dendritic compartment and/or in the axon. In primary hippocampal neurons where human tau was over-expressed both in the somato-dendritic compartment and the axon, the pathological epitopes recognized by the antibodies AT8 (S199/S202/T205), AT100 (T212/S214/T217), and AT180 (T231/S235) were found in the somato-dendritic compartment but not in the axon where tau was either not phosphorylated (T205 and T217) or not simultaneously phosphorylated (T231 and S235) at sites included in the above epitopes. When transfected neurons were treated with the phosphatase inhibitor, okadaic acid, AT8, AT100 and AT180 epitopes were observed in the axon, indicating that tau was dephosphorylated at selective sites of pathological epitopes in this compartment. Expression of tau mutants where one phosphorylation site included in the above epitopes was mutated in alanine showed that the formation of one of these epitopes was not required for the formation of the two others in primary hippocampal neurons. All together our results indicate that in the somato-dendritic compartment, the kinase and phosphatase activity does not prevent the formation of pathological epitopes whereas in the axon, the amount of tau phosphorylated at the pathological epitopes is regulated by phosphatase activity, most likely that of phosphoserine/phosphothreonine phosphatase 2A, the major tau phosphatase. This indicates that if the pathological epitopes are initially formed in the axon in Alzheimer’s disease brain, the activation of phosphatases could be an efficient way to abolish their generation.

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Available from: Nicole Leclerc, Jul 30, 2014
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    • "This may explain Tau accumulation in dendrites in AD and other neurodegenerative Tauopathies. Consistent with this idea, previous studies showed that phosphatases in the somatodendritic compartment dephosphorylate Tau less efficiently than in axonal compartments (Bertrand et al, 2010). However, where and under what conditions hyperphosphorylation of Tau occurs remains unknown . "
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    ABSTRACT: In this issue of The EMBO Journal, Li et al (2011) show that the axon initial segment (AIS) functions as a retrograde trafficking barrier, or axonal rectifier, to exclude axonal Tau from re-entry into the somatodendritic compartment. They elucidate the molecular basis of this rectification by showing that hyperphosphorylation of Tau permits it to detach from microtubules (MTs) and bypass the retrograde barrier.
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    ABSTRACT: Alzheimer's disease is a progressive neurodegenerative disease that is characterized histopathologically by the presence of plaques, mainly composed of Abeta amyloid and the tangles, mainly composed of hyperphosphorylated tau. To date, there is no treatment that can reverse the disease, and all the current therapeutics is directed to cope with the symptoms of the disease. Here we describe the efforts dedicated to attack the plaques and, in more detail, the process of neurofibrillary degeneration, linked to the presence of the hyperphosphorylated microtubule associated protein tau. We have identified the different putative targets for therapeutics and the current knowledge on them.
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    ABSTRACT: We present here the characterization of the epitope recognized by the AT180 monoclonal antibody currently used to define an Alzheimer's disease (AD)-related pathological form of the phosphorylated Tau protein. Some ambiguity remains as to the exact phospho-residue(s) recognized by this monoclonal: pThr231 or both pThr231 and pSer235. To answer this question, we have used a combination of nuclear magnetic resonance (NMR) and fluorescence spectroscopy to characterize in a qualitative and quantitative manner the phospho-residue(s) essential for the epitope recognition. Data from the first step of NMR experiments are used to map the residues bound by the antibodies, which were found to be limited to a few residues. A fluorophore is then chemically attached to a cystein residue introduced close-by the mapped epitope, at arginine 221, by mutagenesis of the recombinant protein. The second step of Förster resonance energy transfer (FRET) between the AT180 antibody tryptophanes and the phospho-Tau protein fluorophore allows to calculate a dissociation constant Kd of 30 nM. We show that the sole pThr231 is necessary for the AT180 recognition of phospho-Tau and that phosphorylation of Ser235 does not interfere with the binding.
    No preview · Article · Aug 2011 · Biochemical and Biophysical Research Communications
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