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. 2013;8(1):e51965.
doi: 10.1371/journal.pone.0051965. Epub 2013 Jan 23.

Accumulation of intraneuronal β-amyloid 42 peptides is associated with early changes in microtubule-associated protein 2 in neurites and synapses

Reisuke H Takahashi  1 , Estibaliz Capetillo-Zarate, Michael T Lin, Teresa A Milner, Gunnar K Gouras
Affiliations

Accumulation of intraneuronal β-amyloid 42 peptides is associated with early changes in microtubule-associated protein 2 in neurites and synapses

Reisuke H Takahashi et al. PLoS One. 2013.

Abstract

Pathologic aggregation of β-amyloid (Aβ) peptide and the axonal microtubule-associated protein tau protein are hallmarks of Alzheimer's disease (AD). Evidence supports that Aβ peptide accumulation precedes microtubule-related pathology, although the link between Aβ and tau remains unclear. We previously provided evidence for early co-localization of Aβ42 peptides and hyperphosphorylated tau within postsynaptic terminals of CA1 dendrites in the hippocampus of AD transgenic mice. Here, we explore the relation between Aβ peptide accumulation and the dendritic, microtubule-associated protein 2 (MAP2) in the well-characterized amyloid precursor protein Swedish mutant transgenic mouse (Tg2576). We provide evidence that localized intraneuronal accumulation of Aβ42 peptides is spatially associated with reductions of MAP2 in dendrites and postsynaptic compartments of Tg2576 mice at early ages. Our data support that reduction in MAP2 begins at sites of Aβ42 monomer and low molecular weight oligomer (M/LMW) peptide accumulation. Cumulative evidence suggests that accumulation of M/LMW Aβ42 peptides occurs early, before high molecular weight oligomerization and plaque formation. Since synaptic alteration is the best pathologic correlate of cognitive dysfunction in AD, the spatial association of M/LMW Aβ peptide accumulation with pathology of MAP2 within neuronal processes and synaptic compartments early in the disease process reinforces the importance of intraneuronal Aβ accumulation in AD pathogenesis.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Aβ42 peptide accumulation and MAP2 reduction in Tg2576 mouse brains with aging.
(A) Aggregation-state specificity of Aβ42 antibody (AB5078P) using gel electrophoresis and Western blot. The sample in the Western blot is in vitro aggregated synthetic Aβ1–42 polypeptide. The Aβ42 antibody prominently detected Aβ1–42 monomers and some low molecular weight oligomers (M/LMW) but not high molecular weight (HMW) oligomers (right lane). In contrast, Aβ antibody 6E10 detected M/LMW and HMW Aβ1–42 oligomers (left lane). (B) M/LMW Aβ42 peptides and MAP2 immunofluorescence in rostral CA1 hippocampal subregions. Tg2576 mouse brains were double labeled with antibodies against M/LMW Aβ42 (green) and MAP2 (red). Accumulation of M/LMW Aβ42 peptides correlated with reduced MAP2-immunoreactivity in CA1 with aging in Tg2576 mice between 2 and 17-months of age. MAP2 reduction was especially apparent in CA1 stratum lacunosum-moleculare (SLM, asterisks) and some reduction was also observed in the stratum radiatum (SR). MAP2 reduction was remarkable at the site where amyloid plaques were formed (arrows). Abbreviations: SO, stratum oriens; PCL, pyramidal cell layer; SR, stratum radiatum; SLM, stratum lacunosum-moleculare. Scale bar: 80 µm. (C) Representative images of the SR of the CA1 region of hippocampus demonstrated reduced MAP2 immunoperoxidase staining with aging (2, 9 and 18 months of age) in Tg2576 compared to wild-type mouse brains. Scale bar: 50 µm. (D) Quantification of MAP2-immunoreactivity in the SR of the hippocampal CA1 region revealed an age-related decrease in Tg2576 with aging at 9–11 and 17–18 months compared to at 2–3 months. Ratio of MAP2-immunoreactivity in the SR region of Tg2576 divided by that of wild-type mice were calculated at 2–3, 9–11, and 17–18 month-old mice, respectively. The ratio was standardized to 100% for MAP2-immunoreactivity of wild-type mouse. A comparison was performed between 2–3 months and 9–11 months, and 2–3 months and 17–18 months of age (Student's t test, * denotes significance: p<0.05).
Figure 2
Figure 2. Accumulation of M/LMW Aβ42 peptides in dendrites correlates with reduced MAP2 in Tg2576 mouse brain by immuno-EM.
(A) Representative image from an area not adjacent to amyloid plaques in a 26-month-old Tg2576 mouse. Marked M/LMW Aβ42 peptide (gold particles, white arrowheads) accumulation was locally associated with reduced MAP2 (immunoperoxidase, white thin arrows) staining in a postsynaptic compartment (plus), while a strongly MAP2 labeled dendritic postsynaptic compartment revealed no Aβ42 labeling (black arrowheads). Moreover, another synaptic compartment revealed intermediate levels of both M/LMW Aβ42- and MAP2-immunoreactivities (asterisk). Synaptic compartments are clearly recognizable because of the presence of postsynaptic densities (black thin arrows). (B) Adjacent to dystrophic neurites (asterisk), M/LMW Aβ42 peptide (gold particles, white arrowheads) accumulation is apparent in dendrites (thick black arrows) with reduced labeling of MAP2 (immunoperoxidase, white thin arrows). (C) Aβ42 peptide (gold particles, white arrowheads) associated with dark fibril-like material (black thin arrow) attach to an abnormal appearing multivesicular body (thick black arrow) in a weak MAP2-labeled dendrite. (D) Marked accumulation of Aβ42-immunoreactivity (gold particles, white arrowheads) in degenerated pre- and postsynaptic compartments without any obvious cytoskeletal structure (thick black arrows) close to amyloid fibers (asterisk). In contrast, a normal MAP2-labeled postsynaptic compartment without M/LMW Aβ42 peptide labeling is located nearby (black arrowheads). Scale bars: 500 nm.
Figure 3
Figure 3. Lack of co-localization of HMW Aβ42 oligomers or thioflavin S-positive plaques with MAP2.
(A) 26-month-old Tg2576 brain sections stained with Aβ42 (green) and MAP2 (red) antibodies. Top: MAP2-immunoreactivity was absent around an Aβ42 plaque (arrowhead). Bottom: A large MAP2-positive dendrite (∼56 µm2, asterisk) with M/LMW Aβ42 peptide accumulation in a higher magnification image of the rectangle in the top panel. (B) In contrast to M/LMW Aβ42 peptides, HMW Aβ42 oligomers detected by M16 antibody did not co-localize with MAP2, even in very small HMW Aβ42 oligomer accumulations (thin arrows). (C) Thioflavin S (ThS) staining for β-pleated Aβ fibrils never revealed co-localization with MAP2. Scale bars, 80 µm (A, top); 20 µm (A, bottom); 100 µm (B and C).
Figure 4
Figure 4. Schematic diagram of proposed sequence of Aβ42, MAP2 and tau alterations in a CA1 pyramidal cell apical dendrite with aging.
At top (I), normal dendrite contains MAP2 associated with microtubules and M/LMW Aβ42 peptides. Cross section taken through the distal apical dendrite (stratum lacunosum-moleculare, SLM) is shown at right. (II) With aging, M/LMW Aβ42 peptides accumulate, which coincides with early reductions in MAP2, especially in the SLM. Later on in Tg2576 mice, Aβ42 M/LMW peptides co-localize with hyperphosphorylated tau in distal processes and synaptic compartments; this co-localization is more prominent in 3×Tg mice (23). (III) Subsequently, Aβ42 HMW oligomers develop in the distal dendrite, which is associated with localized absence of MAP2. Concomitantly, Aβ42 M/LMW peptides further accumulate in more proximal regions of the dendrite. (IV) This is followed by Aβ fibril formation, especially in distal neurites of the SLM and (V) deposition of amyloid plaques in SLM.
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References

    1. Walsh DM, Selkoe DJ (2004) Deciphering the Molecular Basis of Memory Failure in Alzheimer's Disease. Neuron 44: 181–193. - PubMed
    1. Busciglio J, Pelsman A, Wong C, Pigino G, Yuan M, et al. (2002) Altered Metabolism of the Amyloid β Precursor Protein Is Associated with Mitochondrial Dysfunction in Down's Syndrome. Neuron 33: 677–688. - PubMed
    1. Cataldo AM, Petanceska S, Terio NB, Peterhoff CM, Durham R, et al. (2004) Aβ localization in abnormal endosomes: association with earliest Aβ elevations in AD and Down syndrome. Neurobiol Aging 25: 1263–1272. - PubMed
    1. D'Andrea MR, Nagele RG, Wang HY, Peterson PA, Lee DHS (2001) Evidence that neurones accumulating amyloid can undergo lysis to form amyloid plaques in Alzheimer's disease. Histopathology 38: 120–134. - PubMed
    1. Echeverria V, Cuello AC (2002) Intracellular A-beta amyloid, a sign for worse things to come? Mol Neurobiol 26: 299–316. - PubMed

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