Lai Zelin, Gu Lingling, Yu Lu, Chen Huifen, Yu Zhenhua, Zhang Cheng, Xu Xiaoqing, Zhang Mutian, Zhang Min, Ma Mingliang, Zhao Zheng, Zhang Jun
Key Laboratory of Brain Functional Genomics (East China Normal University), Ministry of Education, School of Life Sciences, East China Normal University, Shanghai, 200062 China.
Comprehensive Department of Traditional Chinese Medicine, Putuo Hospital, Affiliated to Shanghai University of Traditional Chinese Medicine, Shanghai, 200062 China.
Cell Biosci. 2020 Jun 15;10:79. doi: 10.1186/s13578-020-00441-z. eCollection 2020.
Ischemic stroke poses a severe risk to human health worldwide, and currently, clinical therapies for the disease are limited. Delta opioid receptor (DOR)-mediated neuroprotective effects against ischemia have attracted increasing attention in recent years. Our previous studies revealed that DOR activation by [d-Ala2, d-Leu5] enkephalin (DADLE), a selective DOR agonist, can promote hippocampal neuronal survival on day 3 after ischemia. However, the specific molecular and cellular mechanisms underlying the DOR-induced improvements in ischemic neuronal survival remain unclear.
We first detected the cytoprotective effects of DADLE in an oxygen-glucose deprivation/reperfusion (OGD/R) model and observed increased viability of OGD/R SH-SY5Y neuronal cells. We also evaluated changes in the DOR level following ischemia/reperfusion (I/R) injury and DADLE treatment and found that DADLE increased DOR levels after ischemia in vivo and vitro. The effects of DOR activation on postischemic autophagy were then investigated, and the results of the animal experiment showed that DOR activation by DADLE enhanced autophagy after ischemia, as indicated by elevated LC3 II/I levels and reduced P62 levels. Furthermore, the DOR-mediated protective effects on ischemic CA1 neurons were abolished by the autophagy inhibitor 3-methyladenine (3-MA). Moreover, the results of the cell experiments revealed that DOR activation not only augmented autophagy after OGD/R injury but also alleviated autophagic flux dysfunction. The molecular pathway underlying DOR-mediated autophagy under ischemic conditions was subsequently studied, and the in vivo and vitro data showed that DOR activation elevated autophagy postischemia by triggering the AMPK/mTOR/ULK1 signaling pathway, while the addition of the AMPK inhibitor compound C eliminated the protective effects of DOR against I/R injury.
DADLE-evoked DOR activation enhanced neuronal autophagy through activating the AMPK/mTOR/ULK1 signaling pathway to improve neuronal survival and exert neuroprotective effects against ischemia.
缺血性中风在全球范围内对人类健康构成严重威胁，目前该疾病的临床治疗方法有限。近年来，δ阿片受体（DOR）介导的抗缺血神经保护作用受到越来越多的关注。我们之前的研究表明，选择性DOR激动剂[d-Ala2，d-Leu5]脑啡肽（DADLE）激活DOR可促进缺血后第3天海马神经元的存活。然而，DOR诱导缺血性神经元存活改善的具体分子和细胞机制仍不清楚。
我们首先在氧糖剥夺/再灌注（OGD/R）模型中检测了DADLE的细胞保护作用，观察到OGD/R SH-SY5Y神经元细胞的活力增加。我们还评估了缺血/再灌注（I/R）损伤和DADLE处理后DOR水平的变化，发现DADLE在体内和体外缺血后均增加了DOR水平。然后研究了DOR激活对缺血后自噬的影响，动物实验结果表明，DADLE激活DOR可增强缺血后的自噬，表现为LC3 II/I水平升高和P62水平降低。此外，自噬抑制剂3-甲基腺嘌呤（3-MA）消除了DOR对缺血性CA1神经元的保护作用。此外，细胞实验结果表明，DOR激活不仅增强了OGD/R损伤后的自噬，还减轻了自噬流功能障碍。随后研究了缺血条件下DOR介导自噬的分子途径，体内和体外数据表明，DOR激活通过触发AMPK/mTOR/ULK1信号通路提高缺血后自噬，而添加AMPK抑制剂化合物C消除了DOR对I/R损伤的保护作用。
DADLE诱发的DOR激活通过激活AMPK/mTOR/ULK1信号通路增强神经元自噬，从而改善神经元存活并对缺血发挥神经保护作用。
