Role of Rac1 GTPase in NADPH oxidase activation and cognitive impairment following cerebral ischemia in the rat.
BACKGROUND
Recent work by our laboratory and others has implicated NADPH oxidase as having an important role in reactive oxygen species (ROS) generation and neuronal damage following cerebral ischemia, although the mechanisms controlling NADPH oxidase in the brain remain poorly understood. The purpose of the current study was to examine the regulatory and functional role of the Rho GTPase, Rac1 in NADPH oxidase activation, ROS generation and neuronal cell death/cognitive dysfunction following global cerebral ischemia in the male rat.


RESULTS
Our studies revealed that NADPH oxidase activity and superoxide (O(2)(-)) production in the hippocampal CA1 region increased rapidly after cerebral ischemia to reach a peak at 3 h post-reperfusion, followed by a fall in levels by 24 h post-reperfusion. Administration of a Rac GTPase inhibitor (NSC23766) 15 min before cerebral ischemia significantly attenuated NADPH oxidase activation and O(2)(-) production at 3 h after stroke as compared to vehicle-treated controls. NSC23766 also attenuated "in situ" O(2)(-) production in the hippocampus after ischemia/reperfusion, as determined by fluorescent oxidized hydroethidine staining. Oxidative stress damage in the hippocampal CA1 after ischemia/reperfusion was also significantly attenuated by NSC23766 treatment, as evidenced by a marked attenuation of immunostaining for the oxidative stress damage markers, 4-HNE, 8-OHdG and H2AX at 24 h in the hippocampal CA1 region following cerebral ischemia. In addition, Morris Water maze testing revealed that Rac GTPase inhibition after ischemic injury significantly improved hippocampal-dependent memory and cognitive spatial abilities at 7-9 d post reperfusion as compared to vehicle-treated animals.


CONCLUSIONS
The results of the study suggest that Rac1 GTPase has a critical role in mediating ischemia/reperfusion injury-induced NADPH oxidase activation, ROS generation and oxidative stress in the hippocampal CA1 region of the rat, and thus contributes significantly to neuronal degeneration and cognitive dysfunction following cerebral ischemia.
Raz
Limor
L
Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia, USA.
Zhang
Quan-Guang
QG
Zhou
Cai-feng
CF
Han
Dong
D
Gulati
Priya
P
Yang
Li-cai
LC
Yang
Fang
F
Wang
Rui-min
RM
Brann
Darrell W
DW
D000818:Animals; D002545:Brain Ischemia / Q000201:enzymology* / Q000378:metabolism / Q000523:psychology*; D003071:Cognition; D004195:Disease Models, Animal; D004789:Enzyme Activation; D006624:Hippocampus / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D008297:Male; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D018384:Oxidative Stress; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
D017382:Reactive Oxygen Species; D019255:NADPH Oxidases; C499134:Rac1 protein, rat; D020830:rac1 GTP-Binding Protein