PolgA D257A mutation does not affect levels of Aβ generating enzymes in APP/Ld mice. 15 μg of brain homogenates from D257A; APP/Ld, D257A, APP/Ld, and wild type mice were loaded per lane and subjected to immunoblot analysis. Immunoblot signals were normalized to the Ponceau S staining intensity for a given lane. The numbers on the immunoblot correspond to mice with specific genotypes as denoted in the legend key (box). (A) BACE1 protein runs at ~68 kDa. (B) BACE1 immunosignals in (A) were expressed as the percentage of the mean wild-type mouse BACE1 immunosignal. Note that BACE1 levels are significantly higher in APP/Ld monogenic and D257A; APP/Ld bigenic mice compared to D257A and wild type non-transgenic mice. BACE1 levels are not altered by the presence of the D257A mutation (mean ± SEM; **p < 0.01; ***p < 0.001; One-way ANOVA followed by Newman–Keuls multiple-comparisons post hoc test). (C) APP processing was determined by measuring levels of both APP C-terminal fragments (C83 & C99) via immunoblot using a rabbit monoclonal antibody that recognizes the C-terminus of APP. Note however, that these C-terminal fragments were below the level of immunoblot detection in non-transgenic APP mouse brains. (D) The ratio of C99:C83, which is directly proportional to the fraction of APP cleaved by BACE1, is not altered by the presence of the D257A mutation. Separate quantification of C83 (E) and C99 (F), normalized to Ponceau S, also show that α- and β-secretase activities are not altered independently of one another by the D257A mutation. (G) PS1 protein levels were measured by immunoblot analysis using a PS1 N-terminal antibody. (H) PS1 immunosignals in (G) were expressed as the percentage of the mean wild-type control PS1 level. PS1-NTF levels are not altered in the presence of the D257A mutation or the APP/Ld transgene.