Remote ischemic postconditioning protects the brain from focal ischemia/reperfusion injury by inhibiting autophagy through the mTOR/p70S6K pathway

Objective: Remote ischemic postconditioning (RIPostC) has been recognized as an applicable strategy for protecting against cerebral ischemia/reperfusion (I/R) injury. This study was performed to examine the effect of RIPostC on cerebral I/R and to explore its underlying mechanism. Methods: Healthy male SD rats (N = 36) were assigned randomly into 3 groups of 12 each: sham group, I/R model group and RIPostC group. Animal models were performed by filament insertion for 2 h with middle cerebral artery occlusion(MCAO) followed by 24 h of reperfusion. RIPostC was induced by 15 min occlusion of femoral arteries followed by 15 min of reperfusion for 3 cycles at the beginning of middle cerebral artery reperfusion. The neurological deficits, infarct size and brain edema were determined. Autophagy was examined by transmission electron microscopy (TEM). The protein levels of microtubule-associated protein light chain 3 (LC3-II), mammalian target of rapamycin (mTOR), serine/threonine kinase p70S6 kinase (p70S6K), and their phosphorylation (p-mTOR and p-p70S6K) in the brain tissue of the rats were determined by western blotting. Results: Our results suggested that RIPostC significantly reduced I/R-induced brain injury, as exhibited by a significantly decreased infarct size, mitigated brain edema and improved neurological deficits. RIPostC also significantly reduced the LC3-II/LC3-I ratio and protein expression of Beclin 1. Much less severe neuronal injury and fewer autophagosomes were observed by TEM in the RIPostC group. Conclusions: These results suggest that RIPostC attenuates cerebral I/R injury by inhibiting autophagy through the activation of the mTOR/p70S6K signaling pathway. Abbreviations: RIPostC: remote ischemic postconditioning; I/R: ischemia/reperfusion; MCAO: middle cerebral artery occlusion; TEM: transmission electron microscopy; IPostC: ischemic postconditioning; IPC: ischemic preconditioning; RIPerC: remote ischemic preconditioning; PI3K: phosphatidylinositol-3-kinase; Akt: protein kinase B; mTOR: Mammalian target of rapamycin; p70S6K: serine/threonine kinase p70S6 kinase