Effects Of MTOR Signaling Pathway On Ischemia-reperfusion Injury In Rats

Objective:Cerebral ischemia is a serious disease which leads to extensive cerebral damage and serious neurological deficits. Till now, tissue plasminogen activator (tPA) remains the only approved drug proven to improve clinical outcome with ischemic stroke. However, the use of tPA is limited because of an increased risk of hemorrhage few hours post-stroke. Therefore, it is urgent for investigating new therapeutic strategies for ischemic stroke. Mammalian target of rapamycin (mTOR) is a critical regulator of cell growth and metabolism that is implicated in many diseases. Rapamycin, an inhibitor of mTOR, was discovered to antagonize the anti-apoptotic signals and stimulate autophagy to maintain normal cell metabolism. It has also demonstrated effects in behavioral and learning in the animal model of traumatic brain injury. However, the effect and mechanism of mTOR-mediated protection in ischemic stroke is unclear. In the present study, we explored whether the mTOR signaling pathway is involved in ischemia-reperfusion injury in SD rats. Methods:We carried out middle cerebral artery occlusion (MCAO) with suture method in SD rats to mimic the process of human cerebral ischemia. The neurological criterion of rats at different time points after MCAO modeling was monitored. The changes of the mTOR signaling pathway in different time point and brain area were detected using Western Blot after MCAO modeling. TTC staining was used to analyze the infarct size before and after modeling. FJB staining was carried out to measure apoptotic cells. CD68 fluorescent staining was used to measure the number of microglial cell. Results:mTOR pathway was activated 60 minutes after MCAO in the ischemic penumbra. As we set ischemic time for 1 h and observed mTOR pathway at different intervals of reperfusion, we found that activation of mTOR pathway kept at higher level from 6h hours after perfusion. Long-term monitoring after ischemia showed that mTOR signaling pathway still kept at high level from 2 weeks. Pre-administration and post-administration of rapamycin significantly improved neurological function deficit and inhibited ischemia-reperfusion-induced mTOR activation at 3 mg/kg for 3 days. Furthermore, rapamycin treated before or after modeling significantly reduced infarct size as well as the number of apoptotic cells and microglial cells. Conclusions:mTOR signaling pathway is activated in cerebral ischemia-reperfusion in acute and chronic phase in rats. mTOR inhibitor rapamycin significantly improves cerebral ischemia-reperfusion injury by reducing the number of cells apoptosis and microglial cells. Its mechanism needs to be further explored.