Figure 4

Mth1/Ogg1 knockout in 3xTg-AD-H mice increases accumulation of 8-oxoG in microglial nuclear DNA and causes microglial activation. (a) Immunohistochemical detection of 8-oxo-dG in nuclei or mitochondria in the cortex of 4–5-month-old ADH/WT and ADH/TO-DKH mice. RNase/HCl: RNase-treated sections were further pretreated with 2 N HCl to detect 8-oxo-dG in nDNA. RNase: sections were pretreated with RNase only to detect 8-oxo-dG in mtDNA. Scale bar = 100 µm. Graphs show the relative 8-oxo-dG IRs (8-oxo-dG index) in the region enclosed by the dotted line. RNase/HCl (n = 4): Wilcoxon exact test (two-sided), *p = 0.0286. RNase (n = 4): Wilcoxon exact test (two-sided), *p = 0.0286. (b) Immunohistochemical detection of 8-oxo-dG in nuclei and mitochondria in the DG of ADH/WT and ADH/TO-DKH mice. Scale bar = 100 µm. Graphs show the relative 8-oxo-dG index in the nuclei (RNase/HCl), and mitochondria (RNase) in the DG. RNase/HCl (n = 4): Wilcoxon exact test (two-sided), *p = 0.0286. RNase (n = 4): Wilcoxon exact test (two-sided), p = 0.2. (c) Damaged neurons accumulate higher levels of 8-oxoG in mtDNA than in nDNA under oxidative conditions in the brain, while activated microglia mainly accumulate 8-oxoG in nuclear DNA. The former causes mitochondrial dysfunction and calpain-dependent neuronal dysfunction, and the latter results in poly (ADP-ribose) polymerase (PARP)-dependent activation of apoptosis-inducing factor (AIF) and exacerbated microgliosis. (d) Immunodetection of CD68. Scale bar = 50 µm. Graphs show the CD68 index. n = 4. Wilcoxon exact test (two-sided), *p = 0.0286. (e) Nuclear 8-oxo-dG was mostly detected in Iba1-positive microglia in the ADH/TO-DKH cortex. Scale bar = 20 µm.