Age-related amyloid beta deposition in transgenic mice overexpressing both Alzheimer mutant presenilin 1 and amyloid beta precursor protein Swedish mutant is not associated with global neuronal loss

Abstract

To analyze the relationship between the deposition of amyloid beta peptides (Abeta) and neuronal loss in transgenic models of Alzheimer's disease (AD), we examined the frontal neocortex (Fc) and CA1 portion of hippocampus (CA1) in PSAPP mice doubly expressing AD-associated mutant presenilin 1 (PS1) and Swedish-type mutant beta amyloid precursor protein (APPsw) by morphometry of Abeta burden and neuronal counts. Deposition of Abeta was detected as early as 3 months of age in the Fc and CA1 of PSAPP mice and progressed to cover 28.3% of the superior frontal cortex and 18.4% of CA1 at 12 months: approximately 20- (Fc) and approximately 40- (CA1) fold greater deposition than in APPsw mice. There was no significant difference in neuronal counts in either CA1 or the frontal cortex between nontransgenic (non-tg), PS1 transgenic, APPsw, and PSAPP mice at 3 to 12 months of age. In the PSAPP mice, there was disorganization of the neuronal architecture by compact amyloid plaques, and the average number of neurons was 8 to 10% fewer than the other groups (NS, P > 0.10) in CA1 and 2 to 20% fewer in frontal cortex (NS, P = 0.31). There was no loss of total synaptophysin immunoreactivity in the Fc or dentate gyrus molecular layer of the 12-month-old PSAPP mice. Thus, although co-expression of mutant PS1 with Swedish mutant betaAPP leads to marked cortical and limbic Abeta deposition in an age-dependent manner, it does not result in the dramatic neuronal loss in hippocampus and association cortex characteristic of AD.

Figure 1.

Age-related Aβ deposition in PSAPP and APPsw transgenic mice. Six-micron paraffin sections of frontal neocortices from PSAPP mice at ages of 3 months (A), 6 months (B), 9 months (C), and 12 months (D), as well as those of APPsw mice at 9 months (E) and 12 months (F) were immunostained with the anti-Aβ antibody 9204. Original magnification: ×173. G: Morphometric analysis of amyloid burden in PSAPP and APPsw transgenic mice. Percentage of amyloid burden (= percentage of total area covered by Aβ immunoreactivity) ± SE in the frontal neocortices of PSAPP (left column, gray) and APPsw (right column, red) mice is shown.

Figure 2.

Phosphorylated τ-positive neurites around cored plaques in 12-month-old PSAPP mice. Fc from 12-month-old PSAPP mice immunostained with a polyclonal antibody AP422 that reacts with an AD-specific phosphorylated τ epitope.

Figure 3.

Regional Aβ deposition in 12-month-old PSAPP and APPsw transgenic mice. Low-power view of 40-μm coronal sections from 12-month-old PSAPP (A) and APPsw transgenic mice (B) immunostained with the anti-Aβ antibody bi-3D6. Scale bar, 1 mm. C: Percentage of amyloid burden ± SE in cingulate cortex (cing), entorhinal cortex (erc), molecular layer of dentate gyrus (dg), and CA1 of PSAPP (left column, gray) and APPsw (right column, red) mice.

Figure 4.

Neuron counts in the frontal neocortices of PSAPP and control mice. Cresyl violet-stained frontal neocortices of PSAPP (A) and non-tg (B) mice at the age of 12 months. Arrows in A indicate amyloid plaques displacing surrounding neurons. Original magnification: ×105. C: Total neuron number in Fc (both hemispheres) ± SE in PSAPP, APPsw, mt PS1, and non-tg mice is shown. The ANOVA was performed at 3 and 12 months.

Figure 5.

Neuron counts in the hippocampal CA1 subfield of PSAPP and control mice. Cresyl violet-stained CA1 hippocampal subfield of PSAPP (A) and non-tg (B) mice at the age of 12 months. Arrow in A indicates disorganization of surrounding neuronal lamina in the vicinity of a compact plaque; arrowhead in A indicates a glial ring surrounding a compact plaque in the stratum oriens of CA1. Scale bar, 250 μm. C: Total neuron number in the entire CA1 ± SE (one hemisphere) in non-tg, APPsw, mt PS1, and PSAPP mice is shown.

Figure 6.

Synaptophysin immunoreactivity in the molecular layer of the dentate gyrus and CA1. A: Confocal quantitation of synaptophysin immunoreactivity by relative optical density ± SE in the outer (oml), middle (mml), and inner (iml) molecular layers of the dentate gyrus (dg) and superior frontal cortex. B: Synaptophysin immunostaining in frontal cortex of 12-month-old PSAPP mouse shows decreased staining in the core of plaques surrounded by synaptophysin immunoreactive dystrophic terminals (arrows). Scale bar, 100 μm.