Early nuclear translocation of endonuclease G and subsequent DNA fragmentation after transient focal cerebral ischemia in mice

We investigated whether the endonuclease G (endoG) translocated from mitochondria to nucleus after transient focal cerebral ischemia (tFCI), thereby contributed to subsequent DNA fragmentation. Adult male mice were subjected to 60 min of focal cerebral ischemia by intraluminal suture blockade of the middle cerebral artery. Western blot analysis for endoG was performed at various time points of tFCI. Nuclear endoG was detected as early as 4 h after tFCI in the ischemic brain, and correspondingly mitochondrial endoG showed a significant reduction at 4 h after reperfusion (p < 0.01). Immunohistochemistry of endoG confirmed that the nuclear translocation of endoG was detected as early as 4 h after tFCI in the middle cerebral artery (MCA) territory of the ischemic brain. Double immunofluorescent staining with endoG and AIF showed that endoG was predominantly colocalized with AIF at 24 h after tFCI. Double staining with endoG immunohistochemistry and TdT-mediated dUTP-biotin nick end labeling showed a spatial relationship between endoG expression and DNA fragmentation at 24 h after tFCI. These data suggest that the early nuclear translocation of endoG occurs and could induce DNA fragmentation in the ischemic brain after tFCI.