内质网应激诱导线粒体钙超载及线粒体凋亡途径在甲基汞神经毒性中的作用机制

Methylmercury (MeHg) is a cumulative environmental contamination harm human being healthy badly and has strong neurotoxicity. This study is focusing on the abnormal Ca2+ flow under endoplasmic reticulum stress (ERS) condition in neuron, in order to explore the mechanisms of MeHg-induced ERS aggravates mitochondrial Ca2+ overload and mitochondrial apoptosis pathway. We speculate that MeHg would aggravate oxidative stress in neuron by ROS over-generation, which might disturb the unfold protein response (UPR) and ERS pathway in endoplasmic reticulum. The ERS might induce an abnormal Ca2+ flow between endoplasmic reticulum and mitochondria, the acceleration of endoplasmic reticulum Ca2+ release followed by mitochondria Ca2+ uptake would lead to mitochondrial Ca2+ overload. The Ca2+ overload would disrupt mitochondrial permeability transition pore (MPTP), disintegrate the mitochondrial membrane potential (MMP), which could aggravate the release of apoptosis factors such as cytochrome C (Cyt C) and apoptosis-inducing factor (AIF), and then activate caspase-dependent or caspase-independent apoptosis pathways. The rat cerebral cortex neurons were used as the research objects in this research, proposing that the neurons would accelerate endoplasmic reticulum Ca2+ release and mitochondrial Ca2+ uptake under ERS condition, this Ca2+ flow disturbance might play important roles mediating mitochondrial Ca2+ overload and mitochondrial apoptosis pathway activation. The present research might provide theoretical and experimental basis for MeHg neurotoxicity mechanisms exploration and MeHg poisoning prevention.

甲基汞（MeHg）是严重危害人类健康的环境蓄积性污染物。本课题以内质网应激（ERS）条件下细胞内Ca2+异常流动为出发点，目的为进一步明确MeHg通过诱发细胞ERS诱导线粒体Ca2+超载及线粒体凋亡途径的作用机制。我们推测：MeHg加剧神经细胞氧化应激水平，干扰内质网未折叠蛋白应答（UPR）和ERS信号通路。ERS诱使细胞内Ca2+异常流动，加速内质网Ca2+释放及线粒体对胞质内Ca2+的摄取，导致线粒体Ca2+超载，线粒体MPTP异常开放，MMP崩解，加速凋亡相关因子Cyt C及AIF的线粒体释放，从而激活caspase依赖性及非依赖性凋亡途径。本课题以大鼠大脑皮质神经元为研究对象，提出神经元在ERS条件下会加速内质网Ca2+释放及线粒体Ca2+摄取，Ca2+的这种异常流动可能是诱发线粒体Ca2+超载及线粒体凋亡不可忽视的一个方面，为MeHg中毒机制的研究及其防治提供理论和实验依据。

甲基汞（methylmercury，MeHg）是常见的重金属污染物之一，具有环境蓄积性、迁移性、高毒性，经食物链进入人体，易于透过血脑屏障而蓄积于脑内，诱发神经毒性。MeHg主要侵犯中枢神经系统，氧化应激在MeHg毒作用机制中发挥重要的作用，并与其它机制存在广泛而密切的联系。内质网作为细胞内合成蛋白质及糖基化修饰的主要场所，其功能极易被过量自由基诱发的氧化应激所影响。但MeHg所致氧化应激如何干扰内质网功能，进而诱发神经细胞内质网应激反应（ERS），以及ERS通过何种途径介导神经细胞凋亡的机制目前尚不十分明确。ERS过程中Ca2+的异常释放可能是ERS干扰线粒体功能，进而激活凋亡信号转导的主要途径之一。但MeHg是否可以通过诱发ERS引起神经细胞内Ca2+由内质网向线粒体流动，进而导致线粒体Ca2+超载及功能紊乱，目前尚不明确。因此本研究推测MeHg诱发神经细胞氧化应激，干扰内质网UPR和ERS信号通路，加速内质网钙库对Ca2+的释放及线粒体对胞质内Ca2+的摄取，导致线粒体Ca2+超载，加速凋亡相关因子Cyt c及AIF的线粒体释放，从而激活线粒体凋亡途径。基于以上假设，本课题从以下三个方面进行相关机制研究：1、研究MeHg所致氧化应激对内质网UPR和ERS信号通路的影响。2、研究MeHg所致ERS对神经元内质网及线粒体间Ca2+流动的影响。3、探讨ERS条件下，神经元Ca2+异常流动所致线粒体Ca2+超载对线粒体凋亡途径的诱导作用。通过研究发现：1、MeHg能够诱发神经元氧化应激，并活化内质网UPR及ERS信号通路。应用抗氧化剂Trolox预处理后，UPR及ERS活化程度下降，表明氧化应激参与了内质网UPR及ERS信号通路的活化过程。2、ERS条件下会诱发内质网和线粒体间Ca2+异常流动，内质网Ca2+释放及线粒体Ca2+摄取增加。3、内质网和线粒体间Ca2+异常流动会加剧线粒体Ca2+超载，诱导线粒体凋亡信号转导。通过本项目研究，从MeHg诱发氧化应激及ERS反应进而加速细胞内Ca2+重分布来诱导线粒体凋亡途径的角度来研究MeHg致神经细胞凋亡的机制，从而可能为MeHg神经毒作用机制的研究和治疗靶点提供科学的理论及实验依据。