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Melatonin ameliorates cerebral ischemia‐reperfusion injury in diabetic mice by enhancing autophagy via the SIRT1‐BMAL1 pathway

Diabetic brains are more vulnerable to ischemia‐reperfusion injury. Previous studies have proved that melatonin could protect against cerebral ischemia‐reperfusion (CIR) injury in non‐diabetic stroke models; however, its roles and the underlying mechanisms against CIR injury in diabetic mice remain unknown. Streptozotocin‐induced diabetic mice and high‐glucose‐cultured HT22 cells were exposed to melatonin, with or without administration of the autophagy inhibitor 3‐methyladenine (3‐MA) and the specifically silent information regulator 1 (SIRT1) inhibitor EX527, and then subjected to CIR or oxygen‐glucose deprivation/reperfusion operation. We found that diabetic mice showed aggravated brain damage, increased apoptosis and oxidative stress, and deficient autophagy following CIR compared with non‐diabetic counterparts. Melatonin treatment exhibited improved histological damage, neurological outcomes, and cerebral infarct size. Intriguingly, melatonin markedly increased cell survival, anti‐oxidative and anti‐apoptosis effects, and significantly enhanced autophagy. However, these effects were largely attenuated by 3‐MA or EX527. Additionally, our cellular experiments demonstrated that melatonin increased the SIRT1‐BMAL1 pathway‐related proteins' expression in a dose‐dependent manner. In conclusion, these results indicate that melatonin treatment can protect against CIR‐induced brain damage in diabetic mice, which may be achieved by the autophagy enhancement mediated by the SIRT1‐BMAL1 pathway.