心跳骤停-心肺复苏后大脑自噬流受损触发神经细胞死亡的作用及机制

Dysregulation of autophagy contributes to neuronal cell death in several neurodegenerative and traumatic brain injury. Markers of autophagyare also increased after cerebral ischemia-reperfusion induced by cardiac arrest (CA), but its mechanisms and function are not known. Recently studies suggest that autophagy played protective roles in the cerebral ischemia and reperfusion phases, whereas reperfusion after CA stimulates neuronal autophagy activation with Beclin-1 upregulation and is implicated in causing neuronal cell death. We examined autophagic flux through the macroautophagy pathway as a determinant of the discrepant outcomes in neuronal cell death induced by CA. We observed accumulation of autophagosomes in vulnerable sensory cortex neurons at 24h after return of spontaneous circulation ( ROSC). This accumulation was not due to increased initiation of autophagy but rather to a decrease in clearance of autophagosomes, as reflected by accumulation of the autophagic substrate SQSTM1/p62, LC3, Beclin-1. Further, we have found that reactive oxygen species (ROS) and the high level of Beclin -1 may be the key factors of the impaired autophagy flux. In current project, several experiments will be performed to address the hypothesis: the impaired autophagic function caused by ROS and high level Beclin-1 contributes to the neuronal cell death triggered by CA .We will use the methods of morphology and molecular biology to test our hypothesis in vitro and in vivo.We will investigate the following issues : First , the relationship between impaired autophagy flux and increased expression of ROS and the effects of impaired autophagy flux on neuronal survive. Second, effects of the expression of Beclin 1 levels on the transcription of autophagic protein and autophagic flux. Finally, the effects of the Beclin 1 gene partly knockout and/or LAMP2 overexpression on the impaired autophagy flux. We expect this study disclose the relationship between impaired autophagic function and neuronal cell death, and will provide new targets for the treatment of brain damage induced by CA.

心跳骤停（CA）发病凶险，已有研究证实心肺复苏后大脑内自噬过度激活可致神经细胞死亡，但具体机制不明。从自噬小体双层膜合成开始至自噬溶酶体形成的自噬激活全过程称之为自噬流，完整的自噬流可清除受损的蛋白质及细胞器达到细胞保护的作用。我们前期发现大鼠CA后溶酶体蛋白(LAMP2)下调致皮层自噬流受损并触发神经细胞死亡。预实验又发现活性氧簇（ROS）及Beclin-1上调可能是自噬流受损的关键因素。因此推测：CA后ROS及Beclin-1上调致自噬流受损并触发神经细胞死亡。为此，本项目基于前期研究将应用自噬探针等新技术探讨：①CA后ROS上调导致神经细胞自噬流受损及死亡的机制。②Beclin-1的上调及下调对LAMP2的转录及自噬流的影响。③Beclin-1基因部分敲除和/或LAMP2过表达对受损自噬流的修复作用。本研究关注CA后大脑自噬流的改变及分子机制，为寻找治疗CA后脑损伤的药物提供新靶点。

心跳骤停（CA）发病凶险，已有研究证实心肺复苏后大脑内自噬过度激活可致神经细胞死亡，但具体机制不明。从自噬小体双层膜合成开始至自噬溶酶体形成的自噬激活全过程称之为自噬流，完整的自噬流可清除受损的蛋白质及细胞器达到细胞保护的作用。我们前期发现大鼠CA后溶酶体蛋白(LAMP2)下调致皮层自噬流受损并触发神经细胞死亡。预实验又发现活性氧簇（ROS）及Beclin-1上调可能是自噬流受损的关键因素。因此推测：CA后ROS及Beclin-1上调致自噬流受损并触发神经细胞死亡。为此，本项目基于前期研究将应用自噬探针等新技术探讨：①CA后ROS上调导致神经细胞自噬流受损及死亡的机制。②Beclin-1的上调及下调对LAMP2的转录及自噬流的影响。③Beclin-1基因部分敲除和/或LAMP2过表达对受损自噬流的修复作用。通过该项国家自然基金我们研究发现：在心搏骤停-心肺复苏（CA-CPR）后 1 天，模型动物大脑感觉运动皮层损伤加重, 2 天感觉运动皮层受损达到高峰，免 疫荧光显示自噬标志蛋白 LC3b 及 Beclin-1 在 CA-CPR 后 6 小时表达达到高 峰。 CA-CPR 后 1 天泛素蛋白 Ubitiquin 和 p62 表达明显升高，提示自噬流受 损。进一步研究发现 CA-CPR 后 1 天，溶酶体相关蛋白表达明显降低，活力下降，提示自噬流受损与溶酶体功能不全及溶酶体酶表达下降密切相关，该研究亦 同时发现 CA-CPR 后星形胶质细胞中未发现有自噬激活现象。受损的自噬流进一步可使内质网应激增强，导致细胞核 内蛋白转录翻译过程抑制，溶酶体酶表达进一步降低，使自噬流受损加剧，神经细胞清除破损蛋白及细胞器的神经修复功能降低，并出现神经元损伤。研究还发 现 CA-CPR 后大脑中过度增多的氧自由基可以直接抑制溶酶体相关蛋白的表达， 导致自噬溶酶体融合障碍，触发自噬流受损。高水平表达的 Beclin-1 对溶酶体相关蛋白 LAMP2 的表达具有抑 制作用。在 OGD 诱导自噬流受损的神经元细胞中过表达 LAMP2 或轻度抑制 Beclin-1 的表达可以部分逆转自噬流受损和神经元损伤。本研究关注CA后大脑自噬流的改变及分子机制，为寻找治疗CA后脑损伤的药物提供新靶点。