Division of Neurovascular Disease, Neurological Institute, Taipei Veterans General Hospital and School of Medicine, National Yang-Ming University, Taipei, Taiwan.
Free Radic Biol Med. 2012 May 1;52(9):1634-47. doi: 10.1016/j.freeradbiomed.2012.01.030. Epub 2012 Feb 10.
Melatonin has many protective effects against ischemic stroke, but the underlying neuroprotective mechanisms are not fully understood. Our aim was to explore the relationship between melatonin's neuroprotective effects and activation of the MT2 melatonin receptor in a murine ischemic-stroke model. Male ICR mice were subjected to a transient middle cerebral ischemic/reperfusional injury, and melatonin (5 and 10 mg/kg, ip) was administrated once daily starting 2 h after ischemia. More than 80% of the mice died within 5 days after stroke without treatment. Melatonin treatment significantly improved the survival rates and neural functioning with modestly prolonged life span of the stroke mice by preserving blood-brain barrier (BBB) integrity via a reduction in the enormous amount of stroke-induced free radical production and significant gp91(phox) cell infiltration. These protective effects of melatonin were reversed by pretreatment with MT2 melatonin receptor antagonists (4-phenyl-2-propionamidotetralin (4P-PDOT) and luzindole). Moreover, treatment with melatonin after stroke dramatically enhanced endogenous neurogenesis (doublecortin positive) and cell proliferation (ki67 positive) in the peri-infarct regions. Most ki67-positive cells were nestin-positive and NG2-positive neural stem/progenitor cells that coexpressed two neurodevelopmental proteins (adam11 and adamts20) and the MT2 melatonin receptor. RT-PCR revealed that the gene expression levels of doublecortin, ki67, adamts20, and adam11 are markedly reduced by stroke, but are restored by melatonin treatment; furthermore, pretreatment with 4P-PDOT and luzindole antagonized melatonin's restorative effect. Our results support the hypothesis that melatonin is able to protect mice against stroke by activating MT2 melatonin receptors, which reduces oxidative/inflammatory stress. This results in the preservation of BBB integrity and enhances endogenous neurogenesis by upregulating neurodevelopmental gene/protein expression.
褪黑素对缺血性中风具有许多保护作用，但其中的神经保护机制尚不完全清楚。我们的目的是在一个缺血性中风的小鼠模型中探索褪黑素的神经保护作用与其 MT2 褪黑素受体激活之间的关系。雄性 ICR 小鼠接受短暂的大脑中动脉缺血/再灌注损伤，在缺血后 2 小时开始每日一次腹腔内给予褪黑素（5 和 10mg/kg）。未经治疗的中风小鼠超过 80%在 5 天内死亡。褪黑素治疗通过减少大量的中风诱导的自由基产生和显著的 gp91(phox)细胞浸润，显著改善了中风小鼠的生存率和神经功能，适度延长了中风小鼠的寿命，从而维持了血脑屏障（BBB）的完整性。MT2 褪黑素受体拮抗剂（4-苯基-2-丙酰胺四氢萘（4P-PDOT）和卢西酮）预处理可逆转褪黑素的这些保护作用。此外，中风后给予褪黑素治疗可显著增强梗死周围区域的内源性神经发生（双皮质素阳性）和细胞增殖（ki67 阳性）。大多数 ki67 阳性细胞为巢蛋白阳性和 NG2 阳性神经干细胞/祖细胞，这些细胞共表达两种神经发育蛋白（adam11 和 adamts20）和 MT2 褪黑素受体。RT-PCR 显示，双皮质素、ki67、adamts20 和 adam11 的基因表达水平在中风后明显降低，但褪黑素治疗可恢复；此外，4P-PDOT 和卢西酮预处理拮抗了褪黑素的恢复作用。我们的研究结果支持这样一种假说，即褪黑素通过激活 MT2 褪黑素受体来保护小鼠免受中风的侵害，从而减少氧化/炎症应激。这导致 BBB 完整性的保持，并通过上调神经发育基因/蛋白表达来增强内源性神经发生。
