Accelerated Abeta deposition in APPswe/PS1deltaE9 mice with hemizygous deletions of TTR (transthyretin)

Abstract

A cardinal pathological lesion of Alzheimer's disease (AD) is the deposition of amyloid beta (Abeta) in the brain. We previously reported that exposing transgenic mice harboring APPswe/PS1deltaE9 transgenes to an enriched environment resulted in reduced levels of Abeta peptides and deposition, findings that were correlated with an increase in the expression of TTR, encoding transthyretin (TTR). TTR is expressed at high levels in the choroid plexus and known to bind Abeta peptides and modulate their aggregation in vitro and in vivo. To explore the impact of TTR expression on Abeta levels and deposition in vivo, we crossed ceAPPswe/PS1deltaE9 transgenic mice to mice with genetic ablations of TTR. We now report that the levels of detergent-soluble and formic acid-soluble levels of Abeta and deposition are elevated in the brains of ceAPPswe/PS1deltaE9/TTR+/- mice compared with age-matched ceAPPswe/PS1deltaE9/TTR+/+ mice. Moreover, Abeta deposition is significantly accelerated in the hippocampus and cortex of ceAPPswe/PS1deltaE9/TTR+/- mice. Our results strongly suggest that TTR plays a critical role in modulating Abeta deposition in vivo.

Figure 1.

Genetic reduction of TTR elevates steady-state levels of cerebral Aβ in the brains of ceAPPswe/PS1ΔE9 mice. A, B, Levels of detergent-soluble Aβ_X-40 and Aβ_X-42 in brain extracts of ceAPPswe/PS1ΔE9/TTR+/− and ceAPPswe/PS1ΔE9/TTR+/+ mice at 7 month time point. C, D, Levels of formic acid-soluble Aβ_X-40 and Aβ_X-42 in brain extracts of ceAPPswe/PS1ΔE9/TTR+/− and ceAPPswe/PS1ΔE9/TTR+/+ mice at 5 and 7 month time points. The asterisk indicates a significant difference from ceAPPswe/PS1ΔE9/TTR+/+ at p < 0.05 (3–4 animals/group). Error bars represent SE.

Figure 2.

Increased amyloid deposition in the cortex and hippocampus of ceAPPswe/PS1ΔE9/TTR+/−. A, Immunohistochemical analysis of brain sections of APPswe/PS1ΔE9/TTR+/+ (a–c, cortex, 4, 5, and 7 month; d, hippocampus, 7 month) and ceAPPswe/PS1ΔE9/TTR+/− (e, f, cortex, 4, 5, and 7 month; h, hippocampus, 7 month) mice immunolabeled with anti-Aβ 3D6 antibodies. Scale bar, 200 μm. B, Quantitative analysis of volume of amyloid burden in the cortex (a) and the hippocampus (b) of APPswe/PS1ΔE9/TTR+/− versus APPswe/PS1ΔE9/TTR+/+ mice. Volume is in arbitrary units (mean voxel count ± SE). The asterisk indicates a significant difference from ceAPPswe/PS1ΔE9/TTR+/+ at *p < 0.05; **p < 0.01 (4 animals/group). Error bars represent SE. C, Thioflavine S-stained amyloid deposits in the cortex of 5-month-old ceAPPswe/PS1ΔE9/TTR+/− versus 5-month-old ceAPPswe/PS1ΔE9/TTR+/+ mice. Costaining of brain sections with 3D6 antibodies (a, d) and thioflavine S (b, e) and overlap (c, f). Scale bar, 50 μm.

Figure 3.

Western blot analysis of protein extracts of brains of APPswe/PS1ΔE9/TTR+/+ (WT), APPswe/PS1ΔE9/TTR+/− (+/−), or APPswe/PS1ΔE9/TTR−/− (−/−) mice. A, Western blot analysis using anti-TTR antibody. B, APP processing. Lane 1, APP-FL; Lane 2, APP-CTFs; Lane 3, α-tubulin; Lane 4, full-length and soluble APP; Lane 5, soluble Swedish βAPPs.