X11alpha haploinsufficiency enhances Abeta amyloid deposition in Alzheimer's disease transgenic mice - PubMed (original) (raw)

X11alpha haploinsufficiency enhances Abeta amyloid deposition in Alzheimer's disease transgenic mice

Inderjeet Saluja et al. Neurobiol Dis. 2009 Oct.

Abstract

The neuronal adaptor protein X11alpha/mint-1/APBA-1 binds to the cytoplasmic domain of the amyloid precursor protein (APP) to modulate its trafficking and metabolism. We investigated the consequences of reducing X11alpha in a mouse model of Alzheimer's disease (AD). We crossed hAPPswe/PS-1DeltaE9 transgenic (AD tg) mice with X11alpha heterozygous knockout mice in which X11alpha expression is reduced by approximately 50%. The APP C-terminal fragments C99 and C83, as well as soluble Abeta40 and Abeta42, were increased significantly in brain of X11alpha haploinsufficient mice. Abeta/amyloid plaque burden also increased significantly in the hippocampus and cortex of one year old AD tg/X11alpha (+/-) mice compared to AD tg mice. In contrast, the levels of sAPPalpha and sAPPbeta were not altered significantly in AD tg/X11alpha (+/-) mice. The increased neuropathological indices of AD in mice expressing reduced X11alpha suggest a normal suppressor role for X11alpha on CNS Abeta/amyloid deposition.

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Figures

Fig. 1

Fig. 1. Reduced X11α protein in ADtg/X11α(+/−) mouse brain without changes in other X11 family proteins

(A) Immunoblot analysis of X11α in brain homogenates confirmed a reduced level of X11α in AD tg/X11α +/− mice (Lanes 3 and 4) compared to AD tg mice (Lanes 1 and 2), while there was no change in the levels of X11β and X11γ. (B) Semi-quantitative analyses of immunoblots revealed that the X11α band density in brains from AD tg/X11α +/− mice was significantly less (54 %) than in AD tg mice. (C–D) Semi-quantitative analyses of the band density for X11β and X11γ revealed no significant change in the levels of either protein. Error bars indicate S.E.M. (n = 6), and statistically significant differences are indicated (*p < 0.01)

Fig. 2

Fig. 2. Increased C-terminal fragments in AD tg/X11α+/− mice

(A) Immunoblot analysis of APP and the C-terminal fragments C99 (CTFβ) and C83 (CTFα). Proteins (65 μg) from mouse brain homogenates were detected by immunoblot with an antibody to the N-terminus of APP (for detecting full length APP), to the C-terminus of APP (for detecting CTFs), or to β-actin. Protein from cell lysates transfected with C99 (Lane 1) was run as a positive control for detecting the C99 fragment in brain homogenate (B, C, D). Band intensities of total APP, C83 and C99 from AD tg and AD tg/X11α +/− mice were quantified and normalized to the levels of β-actin. X11α haploinsufficiency significantly increased the level of C83 (CTFα) (C) and C99 (CTFβ) (D) without altering the level of total APP (B). Error bars indicate S.E.M. (n = 6), and statistically significant differences are indicated (**p < 0.01 and *p <0.05)

Fig. 3

Fig. 3. Levels of sAPPα and sAPPβ fragments in AD tg/X11α (+/−) mice

Immunoblot analysis of sAPPα and sAPPβ fragments is shown. Proteins (60 μg) from mouse brain homogenates were detected by immunoblot with antibodies to sAPPα, sAPPβ or to β-actin. Conditioned medium (CM) from a CHO (Chinese hamster ovary) cell line stably transfected with APPswe and PS-1ΔE9 mutation was used as a positive control to verify the specificity of the secreted product. (A) Band intensities were quantified and normalized to levels of β-actin. X11α haploinsufficiency does not lead to a statistically significant change in the level of (B) sAPPα and (C) sAPPβ. Error bars indicate S.E.M. (n = 4).

Fig. 4

Fig. 4. Aβ levels in brain are increased by X11α reduction

Measurement of soluble Aβ levels in 12 month old mouse brain homogenates revealed a significant increase in Aβ40 (A), Aβ42 (B), and total Aβ (C) levels in ADtg mice on an X11α haploinsufficient background (n = 4; * indicates p < 0.01). The Aβ42/Aβ40 ratio (D) was not significantly altered.

Fig. 5

Fig. 5. Aβ/amyloid plaque density is increased by X11α reduction

(A) Representative silver-stained sections from the hippocampus and cortex of AD tg mice or of AD tg/X11α haploinsufficient mice revealed a higher plaque density in AD tg mice on a X11α +/− background. Higher magnification images in lower four panels represent insets from the top two panels. Scale bars 150 μ (top panels) and 50 μ (bottom four panels). (B–C) Increased plaque density in hippocampus of ADtg/X11α depleted mice. Stereological counts of amyloid plaque density were obtained from sections from cortex and hippocampus of AD tg versus ADtg/X11α +/− mice at 12 months of age. The total number of plaques in the cortex (B) and hippocampus (C) were calculated for both groups and expressed as total counts per section. The error bars indicate S.E.M (n = 4), and statistically significant differences are indicated (*p < 0.05).

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