Biochemical and behavioral characterization of the double transgenic mouse model (APPswe/PS1dE9) of Alzheimer's disease

Objective The double transgenic mouse model (APPswe/PS1dE9) of Alzheimer's disease (AD) has been widely used in experimental studies. beta-Amyloid (A beta) peptide is excessively produced in AD mouse brain, which affects synaptic function and the development of central nervous system. However, little has been reported on characterization of this model. The present study aimed to characterize this mouse AD model and its wild-type counterparts by biochemical and functional approaches. Methods Blood samples were collected from the transgenic and the wild-type mice, and radial arm water maze behavioral test was conducted at the ages of 6 and 12 months. The mice were sacrificed at 12-month age. One hemisphere of the brain was frozen-sectioned for immunohistochemistry and the other hemisphere was dissected into 7 regions. The levels of A beta(1-40), A beta(1-42) and 8-hydroxydeoxyguanosine (8-OHdG) in blood or/and brain samples were analyzed by ELISA. Secretase activities in brain regions were analyzed by in vitro assays. Results The pre-mature death rate of transgenic mice was approximately 35% before 6-month age, and high levels of A beta(1-40) and A beta(1-42) were detected in these dead mice brains with a ratio of 1: 10. The level of blood-borne A beta at 6-month age was similar with that at 12-month age. Besides, A beta(1-40) level in the blood was significantly higher than A beta(1-42) level at the ages of 6 and 12 months (ratio 2.37: 1). In contrast, the level of A beta(1-42) in the brain (160.6 ng/mg protein) was higher than that of A beta(1-40) (74 ng/mg protein) (ratio 2.17: 1). In addition, the levels of A beta(1-40) and A beta(1-42) varied markedly among different brain regions. A beta(1-42) level was significantly higher than A beta(1-40) level in cerebellum, frontal and posterior cortex, and hippocampus. Secretase activity assays did not reveal major differences among different brain regions or between wild-type and transgenic mice, suggesting that the transgene PS1 did not lead to higher gamma-secretase activity but was more efficient in producing A beta(1-42) peptides. 8-OHdG, the biomarker of DNA oxidative damage, showed a trend of increase in the blood of transgenic mice, but with no significant difference, as compared with the wild-type mice. Behavioral tests showed that transgenic mice had significant memory deficits at 6-month age compared to wild-type controls, and the deficits were exacerbated at 12-month age with more errors. Conclusion These results suggest that this mouse model mimics the early-onset human AD and may represent full-blown disease at as early as 6-month age for experimental studies.