Figure 1.

DNA polymerase β decline causes increased susceptibility to DNA damage in the mouse brain. (A) Diagrammatic representation of study. Mice utilized; Wild type (WT), Polymerase β heterozygous (Polβ), Alzheimer's (AD) transgenic (3xTgAD) and the 3xTgAD/Polβ cross (3xTg/Polβ). Comprehensive behavioral analysis was conducted at 6, 14 and 24 months. (B) Cortex Polβ protein levels in the four mouse lines at the indicated ages. All groups had significantly lower protein levels compared to 6-month WT mice, n = 3, *P < 0.05. Refer to Supplementary Figure S1A for additional information and full images. (C) Neutral comet analysis of designated mouse brain regions shows more DNA strand breaks in 3xTg/Polβ mice at 24 months of age. ****P < 0.001, scale bar = 300 μm. (D) Quantitation of double-stranded break (DSB) foci per cell by γH2AX staining shows increases in only the 3xTg/Polβ mice at 6 months, while all transgenic groups have elevated foci levels at 24 months compared to WT (n = 3 for each set, greater than 50 cells counted per set). Error bars represent mean ± SD. (E) Co-localization between antibodies targeting 53BP1 and γH2AX confirms that these foci mark DNA DSBs. Six month (M) old WT and 3xTgAD/Polβ mice are shown as a representative image. Scale bar = 5 μm. (F) Levels of cleaved caspase-3 in the hippocampus correspond to age, disease and repair deficiency. **P < 0.01, ***P < 0.005, n = 3, multiple sequential sections per animal. Scale bar = 200 μm. (G) Levels of cleaved caspase-3 in the cortex confirm global increase in apoptotic activation in transgenic mice after 14 months, n = 3, multiple sections per animal, scale bar = 200 μm. Error bars represent mean ± standard error of mean (SEM), in all panels and figures unless otherwise specified.