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Labelling by axonal transport of myelin-associated proteins in the rabbit visual pathway.

ABSTRACT: After intraocular injections of [3H]leucine, six regions of the visual pathway of adult rabbit were used to study the spatio-temporal pattern of the slow anterograde axonal transport of radioactive proteins associated with the particulate fraction, the water-soluble fraction and the myelin fraction. Unlike other fractions, myelin-associated labelled proteins represented a time-constant (for a given region) percentage of total tissue radioactivity. This percentage increased from the first half to the second half of the optic nerve and remained high in the chiasma and tract. The peak specific radioactivity of myelin decreased in the same direction. Myelin proteins were separated by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and the labelling patterns obtained in different regions and at different survival times were compared. At the peak of myelin radioactivity of a given region the label was typically associated with four protein bands, L1, L2, L3 and L4, of 40000, 44000, 62000, and 68000 mol.wts. respectively. The basic protein, the proteolipid protein and the W1 component (mol.wt. 51000-53000) of the Wolfgram proteins were not significantly labelled. The radioactivity associated with the W2 component (mol.wt 60000) of the Wolfgram proteins could be derived from the closely migrating L3 component. At shorter survival times no clear labelling pattern could be detected. At longer survival times radioactivity was almost totally localized around band L3. The results presented underline the importance of choosing appropriate experimental conditions to obtain a consistent labelling pattern of myelin-associated proteins and to investigate the possible mechanism responsible for this phenomenon.

SUBMITTER: Giorgi PP

PROVIDER: S-EPMC1163027 | biostudies-other | 1981 May

REPOSITORIES: biostudies-other

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Project description:UNLABELLED:Despite the demonstration that amyloid-? (A?) can trigger increased tau phosphorylation and neurofibrillary tangle (NFT) formation in vivo, the molecular link associating A? and tau pathologies remains ill defined. Here, we observed that exposure of cultured primary neurons to A? trimers isolated from brain tissue of subjects with Alzheimer's disease led to a specific conformational change of tau detected by the antibody Alz50. A similar association was supported by postmortem human brain analyses. To study the role of A? trimers in vivo, we created a novel bigenic Tg-A?+Tau mouse line by crossing Tg2576 (Tg-A?) and rTg4510 (Tg-Tau) mice. Before neurodegeneration and amyloidosis, apparent A? trimers were increased by ?2-fold in 3-month-old Tg-A? and Tg-A?+Tau mice compared with younger mice, whereas soluble monomeric A? levels were unchanged. Under these conditions, the expression of soluble Alz50-tau conformers rose by ?2.2-fold in the forebrains of Tg-A?+Tau mice compared with nontransgenic littermates. In parallel, APP accumulated intracellularly, suggestive of a putative dysfunction of anterograde axonal transport. We found that the protein abundance of the kinesin-1 light chain (KLC1) was reduced selectively in vivo and in vitro when soluble A? trimers/Alz50-tau were present. Importantly, the reduction in KLC1 was prevented by the intraneuronal delivery of Alz50 antibodies. Collectively, our findings reveal that specific soluble conformers of A? and tau cooperatively disrupt axonal transport independently from plaques and tangles. Finally, these results suggest that not all endogenous A? oligomers trigger the same deleterious changes and that the role of each assembly should be considered separately. SIGNIFICANCE STATEMENT:The mechanistic link between amyloid-? (A?) and tau, the two major proteins composing the neuropathological lesions detected in brain tissue of Alzheimer's disease subjects, remains unclear. Here, we report that the trimeric A? species induce a pathological modification of tau in cultured neurons and in bigenic mice expressing A? and human tau. This linkage was also observed in postmortem brain tissue from subjects with mild cognitive impairment, when A? trimers are abundant. Further, this modification of tau was associated with the intracellular accumulation of the precursor protein of A?, APP, as a result of the selective decrease in kinesin light chain 1 expression. Our findings suggest that A? trimers might cause axonal transport deficits in AD.

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Labelling by axonal transport of myelin-associated proteins in the rabbit visual pathway.

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