肝脏脂代谢稳态的转录调节机制研究

Hepatic liver homeostasis relies on the coordination of lipid uptake, synthesis, secretion, and beta-oxidation, the disruption of which leads to fatty liver disease and dyslipidemia and is closely related to insulin resistance. ZBTB20, a zinc finger protein originally identified by the applicant, is essential for the maintenance of glucose and lipid homeostasis in mice. We have previously demonstrated that ZBTB20 regulates hepatic lipogenesis through modulating the expression ChREBP，one of the key transcription factors in liver de novo lipogenesis. In this proposal, we plan to identify the post-translational modifications and cofactors of ZBTB20, so as to determine the biochemical basis and related mechanisms by which ZBTB20 senses nutritional signals, performs cytosolic and nuclear shuttling, and regulates ChREBP gene transcription. Meanwhile, given the fact that deletion of hepatic Zbtb20 results in a much more prominent phenotype of lipid metabolism compared to that of ChREBP, we also plan to elucidate ChREBP-independent mechanisms about the regulation of lipid metabolism by ZBTB20. Put together, these proposed studies will enable us to better understand the role of ZBTB20 in lipid homeostasis in the liver, and shed light on the regulation of liver lipid metabolism, with the potential to develop new therapeutic strategy for fatty liver disease.

肝脏脂代谢稳态的维持有赖于脂质摄取、合成、分泌和氧化利用等关键环节的有机协调，其稳态失衡可导致脂肪肝和血脂紊乱，与胰岛素抵抗密切相关。申请人基因打靶研究显示，自主发现的锌指蛋白ZBTB20是维持机体糖脂代谢稳态的重要分子。在前期已证实ZBTB20调节转录因子ChREBP表达与肝脏脂质合成的基础上，拟从研究蛋白翻译后修饰和共作用分子为切入点，深入解析ZBTB20感受营养信号、核浆穿梭和激活ChREBP基因转录的生化基础与分子机制，揭示ZBTB20调节肝脏脂质合成的信号通路。同时，鉴于肝脏特异性ZBTB20敲除小鼠的脂代谢表型远比ChREBP敲除小鼠严重，拟重点分析ZBTB20调节肝脏脂代谢的非ChREBP依赖途径及其靶基因，从而综合揭示ZBTB20调节肝脏脂代谢稳态的转录调节网络，并明确其在脂肪肝等脂稳态失衡中的病理作用，提出肝脏脂代谢稳态维持的新机制，为脂肪肝的防治提供新的策略和理论依据。

肝脏是调节糖脂代谢稳态的重要器官，其功能失调可导致脂肪肝、血脂紊乱、胰岛素抵抗等。申请人前期自主发现并在国际上率先研究发现肝脏锌指蛋白ZBTB20是维持机体糖脂代谢稳态的重要分子，可通过转录因子ChREBP调节肝脏脂质从头合成。本项目解析了ZBTB20营养感应的分子机制，发现PKA介导的蛋白磷酸化在调节ZBTB20核浆穿梭中发挥重要作用，其中614位丝氨酸磷酸化是其胞浆定位的重要生化基础；比较了肝脏ZBTB20与ChREBP在调节糖脂代谢方面的差异，研究发现肝脏特异性敲除ChREBP导致高果糖饮食诱导的肝糖原合成过度和肝毒性，伴有肝脏糖代谢中间产物G-6-P含量增加和ATP含量下降，这些表型可被过表达ChREBP的靶基因丙酮酸激酶LPK所逆转，由此揭示了肝脏ChREBP调节糖脂代谢稳态的生理功能。另一方面，肝脏特异性ChREBP敲除小鼠并没有出现类似肝脏特异性ZBTB20敲除小鼠（LZB20KO）的低血脂表型，表明存在ZBTB20调节脂代谢稳态存在着非ChREBP依赖途径。研究发现脂蛋白脂肪酶LPL及其分泌的正调节因子SEL1L是肝脏ZBTB20的靶基因，肝脏特异性敲除ZBTB20导致LPL表达水平大幅升高,血LPL含量和活性升高，血脂清除能力显著增强；而敲除肝脏LPL可逆转LZB20KO的低甘油三酯血症表型，从而表明LPL是肝脏ZBTB20调节血甘油三酯稳态的主要靶基因。本项目的研究揭示了肝脏调节脂代谢稳态的新机制，为脂代谢紊乱的防治提供了新的靶标。