Rac1 contributes to cerebral ischemia reperfusion-induced injury in mice by regulation of Notch2

- Inhibition of Rac1 enhances post-ischemic recovery in the short term but not the long term.
- Rac1 activation induced neural cells apoptosis and increased ROS production following cerebral ischemia-reperfusion.
- Rac1 regulates Notch2 signaling following cerebral IR injury in vivo and in vitro.
- Rac1 regulated Notch2 by NFkB activation.
- Activation of Notch2 is involved for the proliferation and self-renewal in neuron stem-like cells.

Background: Cerebral ischemia-reperfusion (IR) injury is a complex pathological process that can cause irreversible brain damage, neuronal injury or death from brain ischemia. Rac1 GTPase is involved in cellular protection from IR injury. However, the mechanism of protection and the molecules affected by Rac1 remain to be defined. Methods and results: C57BL/6 mice were subjected to middle cerebral artery occlusion for 1 h, followed by 24-h reperfusion. In this in vivo model of cerebral IR injury, mice treated with the Rac GTPase inhibitor NSC23766 or Rac1 small interfering RNA (siRNA) had better short-term (72 h) neurologic scores, less infarction volume, higher production of antioxidant enzymes, lower lipid peroxide, and reduced apoptosis compared with a vehicle-treated group or a control-siRNA group. However, long-term (14 day) neurologic scores were worse for the two treatments compared to controls. Microarray and quantitative polymerase chain reaction (PCR) revealed that Notch2 was downregulated under NSC23766 treatment. Notch2 protein levels decreased with NSC23766 and Rac1 siRNA in vitro and in vivo. Cell survival increased with the Notch signaling inhibitor DAPT or Notch2 siRNA and NICD2 attenuated the NSC23766 effect. In addition, immunoblotting showed that DAPT and Notch2 siRNA changed the levels of apoptosis-regulating proteins. NFkB mediated Rac1, which regulated Notch2 in an oxygen glucose deprivation model. Both inhibitors of Notch2 and Rac1 enhanced neural stem cell differentiation. Conclusions: This study demonstrated the importance of Rac1 regulation of Notch2 in mediating cerebral IR-induced production of injurious reactive oxygen species and cell death in vitro and in vivo in the short term. Targeted inhibition of Rac1 or Notch2 is new avenue for in vivo therapy aimed at protecting organs at risk from IR injury.