A The DSBs DNA damage in the OL lineage of human frontal cortex were analysed by γH2AX. Quantifications revealed a significantly increase of DSB-DNA damage in the DEM subjects. B DNA repair enzyme, ATM was found activated (pATMser1981) in the OL (Olig2+) lineage, and a significant upregulation of pATMser1981 in the OL lineage in both GM and WM, in AD (All unpaired t-test, vs NC). To test whether DNA damage was associated with aberrant cell cycle reentry and cell death in the mature OLs, human frontal cortex were analysed by Cyclin D1 and cleaved caspase-3 (CC3). C A significant increase of postmitotic mOL re-expressing Cyclin D1 was found in the GM of the DEM and AD subjects (All unpaired t-test, vs NC). D The cell cycle events (CCE) in intracortical mOL was accompanied by a mild, but not significant, increase of apoptosis in the GM of the DEM and AD subjects. E The gene expression profile of the whole cortex presented in a custergram normalized against clinical phenotype (NC, DEM and AD). Consistent pattern of change between DEM and AD listed on the left. Green, downregulation; red, upregulation.