柠檬酸诱导的线粒体应激与脂肪积累的机理研究

Mitochondrion is an essential organelle. Disruption of mitochondria protein homeostasis leads to mitochondria unfolded protein response (UPRmt), which is associated with aging, neurodegenerative diseases, type 2 diabetes, cancers, etc. Our preliminary results showed that either RNAi knockdown of aco-2 or idha-1 that involve in the tricarboxylic acid cycle (TCA cycle), or dietary supplement with citrate, consistently caused both mitochondria UPRmt and increased lipid accumulation. Therefore, here, we proposed several approaches in order to investigate the underlying mechanisms of citrated induced mitochondria UPRmt and lipid accumulation. First of all, we will search for genes or signaling pathways that response to citrate metabolism through RNA-seq technology, and then explore their biological roles in mitochondria UPRmt and lipid accumulation. Secondly, we will screen factors that genetically or biophysically interact with the transcription factor PHA-4, a sensor of mitochondria UPRmt and nucleolus stress, via the advantages of larger-scale genetic screen and Co-Immunoprecipitation technology. Furthermore, we will uncover how these factors work with PHA-4 in response to citrated induced mitochondria UPRmt and lipid accumulation. Thirdly, we will determine the factors that pass signals of mitochondria UPRmt to cell nuclear, and eventually cause increased lipid accumulation. In summary, these works will provide novel insights into the synergetic regulation of mitochondria UPRmt and lipid accumulation, as well as stress response related metabolic diseases.

线粒体是重要的细胞器。当线粒体的蛋白质稳态发生改变时，引起线粒体非折叠蛋白反应（UPRmt），与衰老、神经退行性疾病、2型糖尿病、癌症等重大疾病的发生发展密切相关。我们前期工作发现，无论是RNAi干扰aco-2或者idha-1阻断三羧酸循环中柠檬酸代谢，还是外源添加柠檬酸，不仅诱导线粒体UPRmt，而且引起脂肪积累。在此基础上，我们提出：1）RNA-seq技术寻找响应柠檬酸作用的基因或信号通路，并研究其功能及作用机理；2）通过遗传筛选、CO-IP技术等寻找与转录因子PHA-4互作的因子，揭示它们与PHA-4共同响应线粒体UPRmt及调控脂肪积累的分子机理；3）寻找介导把柠檬酸诱导的线粒体UPRmt信号传递给细胞核的因子，并揭示其调控UPRmt和脂肪积累的分子机理。本项目的研究将对阐明线粒体应激和能量代谢的协调调控，以及应激相关代谢性疾病机理提供新的视野。

线粒体被认为是细胞的能量工厂，线粒体蛋白质组的动态平衡，即蛋白质稳态（protein homeostasis, proteostasis），对线粒体的功能至关重要。线粒体蛋白质稳态失调会引起线粒体未折叠蛋白反应(UPRmt)，与衰老、神经退行性疾病、2型糖尿病、癌症等重大疾病的发生发展密切相关。三羧酸循环是线粒体能量代谢的重要代谢途径，其功能受到影响时，是否会引起线粒体非折叠蛋白反应（UPRmt），以及如何影响细胞及机体的能量代谢等，此前知之甚少。本项目的研究工作证明了三羧酸(TCA)循环中，分别编码顺乌头酸酶和异柠檬酸脱氢酶的柠檬酸代谢关键酶的编码基因aco-2或idha-1的失活导致胞内柠檬酸积累，特异地诱导UPRmt，并促进脂质积累。并进一步揭示了转录因子DVE-1介导核激素受体NHR-80响应胞内柠檬酸累积诱导的UPRmt，通过与nhr-80的启动子结合反式激活其表达。进而，NHR-80转录激活脂质生成基因dgat-2等的表达，从而促进脂质积累，将累积的柠檬酸转换用于脂质生成和作为三酰甘油储存在脂滴中。该机制揭示了线粒体应激与脂质代谢调控之间的联系，并为了解和认识线粒体功能障碍相关疾病的发生发展机理提供了新的认识和发现。