Reduction of amyloid angiopathy and Abeta plaque burden after enriched housing in TgCRND8 mice: involvement of multiple pathways

Abstract

Diversity and intensity of intellectual and physical activities seem to have an inverse relationship with the extent of cognitive decline in Alzheimer's disease (AD). To study the interaction between an active lifestyle and AD pathology, female TgCRND8 mice carrying human APPswe+ind were transferred into enriched housing. Four months of continuous and diversified environmental stimulation resulted in a significant reduction of beta-amyloid (Abeta) plaques and in a lower extent of amyloid angiopathy. Neither human amyloid precursor protein (APP) mRNA/protein levels nor the level of carboxy-terminal fragments of APP nor soluble Abeta content differed between both groups, making alterations in APP expression or processing unlikely as a cause of reduced Abeta deposition. Moreover, DNA microarray analysis revealed simultaneous down-regulation of proinflammatory genes as well as up-regulation of molecules involved in anti-inflammatory processes, proteasomal degradation, and cholesterol binding, possibly explaining reduced Abeta burden by lower aggregation and enhanced clearance of Abeta. Additionally, immunoblotting against F4/80 antigen and morphometric analysis of microglia (Mac-3) revealed significantly elevated microgliosis in the enriched brains, which suggests increased amyloid phagocytosis. In summary, this study demonstrates that the environment interacts with AD pathology at dif-ferent levels.

Figure 1-6942

A and B: Representative figures of SH (A) and EH (B) plaque burden after immunohistochemical staining against Aβ with 6F/3D antibody, digitization and subsequent extraction of blue to gray values to obtain the best contrast between immunopositive plaques and background. C and D: Number of neocortical and hippocampal plaques and the percentage of Aβ-positive area related to total area of the neocortex and hippocampus. E: Percentage of Aβ-positive vessel walls related to the total amount of counted vessels. Data are given as mean ± SD; statistics, t-test; P′, Bonferroni corrected.

Figure 2-6942

APP expression and processing. A–D: Steady state levels of soluble Aβ_1-40 and Aβ_1-42 as measured by ELISA and Western blot. E: Representative Western blot with antibody specific for Aβ (6E10). There are slight variations in levels of detergent-soluble Aβ_1-40 and Aβ_1-42, but these are fully consistent with the variations observed with a protein loading control, α-tubulin. F: Representative Western blot data showing no differences in full-length APP and in proteolytic fragments of APP (CTFβ). A faint CTFα fragment was only detectable after a longer exposition duration (F*). G–I: Steady state levels of APP mRNA and protein as well as CTFβ stub. No differences were seen in EH versus SH mice. Data are given as means ± SD; statistics, t-test.

Figure 3-6942

A and B: Levels of GFAP and F4/80 antigen in SH and EH mice as measured by Western blot analysis. In contrast to astrocytic marker GFAP, F4/80 antigen was significantly elevated in EH when compared with SH mice. C: Additionally, the number of microglial cells per mm² that were counted after immunohistochemistry against Mac-3 was also increased in EH mice. D: Representative picture of Mac-3 immunostaining (P, plaque) showing ring formation of ramified and elongated microglial cells surrounding and infiltrating the amyloid plaques. Data are given as means ± SD; statistics, t-test. Original magnifications: ×200; ×400 (inset).

Figure 4-6942

Number of genes categorized into different classes concerning their biological function based on Ingenuity Pathway Analysis and literature survey.