Melatonin prevents ischemic brain injury through activation of the mTOR/p70S6 kinase signaling pathway

We previously reported that melatonin prevents neuronal cell death in ischemic brain injury through the activation of Akt and the inhibition of apoptotic cell death. We investigated whether melatonin inhibits the apoptotic signal through the activation of a mammalian target of rapamycin (mTOR) and p70S6 kinase and its downstream target, S6 phosphorylation. It is known that mTOR is a downstream target of Akt and a central regulator of protein synthesis, cell growth, and cell cycle progression. Adult male rats were treated with melatonin (5 mg/kg) or vehicle prior to middle cerebral artery occlusion (MCAO). Brains were collected at 24 h after MCAO and infarct volumes were analyzed. We confirmed that melatonin significantly reduces infarct volume and decreases the number of TUNEL-positive cells in the cerebral cortex. Brain injury induced a decrease in phospho-mTOR and phospho-p70S6 kinase. Melatonin prevented the injury-induced decrease in Akt activation and phosphorylation of mTOR and p70S6 kinases, and the subsequent decrease in S6 phosphorylation. Our results suggest that melatonin prevents cell death resulting from ischemic brain injury and that its neuroprotective effects are mediated by preventing the injury-induced decrease of mTOR and p70S6 kinase phosphorylation.