Aβ42 peptide accumulation and MAP2 reduction in Tg2576 mouse brains with aging.

<p>(A) Aggregation-state specificity of Aβ42 antibody (AB5078P) using gel electrophoresis and Western blot. The sample in the Western blot is <i>in vitro</i> 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 <i>t</i> test, * denotes significance: <i>p</i><0.05).