Figure 5

BACE1-cleaved APP fragments sAPPβ and C99 are reduced in female but not male 5XFAD/BACE1 ^+/− mice. (A) Representative sAPPβ immunoblot and Ponceau S staining of brain homogenates from 4 month-old male (M) and female (F) mice. Note the minimal sAPPβ signal in the 5XFAD/BACE1^−/− lane; residual band likely results from minor cross-reactivity to sAPPα. (B-D) Relative quantifications of sAPPβ immunoblot signals from 5XFAD/BACE1^+/+ and 5XFAD/BACE1^+/− mice. At 4 months of age there is no statistical difference in sAPPβ levels between the sexes or genotypes. However, at 6 and 9 months of age 5XFAD/BACE1^+/− females show trends toward lower sAPPβ levels than 5XFAD/BACE1^+/+ females, mirroring the significant reduction in Aβ42 levels. sAPPβ levels in 6 and 9 month-old 5XFAD/BACE1^+/− and 5XFAD/BACE1^+/+ male are indistinguishable, and significantly less than in 5XFAD/BACE1^+/+ females. (E) Representative of C99 immunoblot and Ponceau S staining of brain homogenates from 9 month-old male (M) and female (F) mice. The doublet bands reflect the phosphorylation state of the APP C-terminal fragments. The lower doublet represents the α-secretase-cleaved APP C-terminal fragment C83. Note the absence of the C99 signal in the 5XFAD/BACE1^−/− lane. (F-H) Relative quantification of C99 immunoblot signals from male and female 5XFAD/BACE1^+/+ and 5XFAD/BACE1^+/− mice. At all ages, 5XFAD/BACE1^+/− females have lower levels of C99 than 5XFAD/BACE1^+/+ females, but this difference reaches statistical significance only at 4 months. In contrast, C99 levels are not significantly different between 5XFAD/BACE1^+/+ and 5XFAD/BACE1^+/− males at any age. At 4 and 6 months of age, 5XFAD/BACE1^+/+ males have significantly less C99 than 5XFAD/BACE1^+/+ females, but at 9 months the decrease does not reach statistical significance due to large variation in the female cohort. Overall, the patterns of sAPPβ and C99 levels correlate with those of Aβ42 levels for the different genotypes and genders.