进食活化ANGPTL3的分子机制及其在血脂异常发生发展中的作用机理研究

ANGPTL3 is a secreted protein that made exclusively in liver and inhibits lipoprotein lipase (LPL) . Genetics data of human and mouse studies showed that loss-of-function mutations of ANGPTL3 cause panhypolipidemia, with very low levels of circulating triglyceride and cholesterol. In our previous work, we found that food intake activates ANGPTL3, which preferentially inhibits LPL activity in oxidative tissues (heart, muscle and brown adipose tissue), and spares triglyceride for white adipose tissue (WAT) uptake and storage. The full activation of ANGPTL3 requires one step protease cleavage at the conserved RxxR motif. The cleaved N terminal domain of ANGPTL3 interacts with ANGPTL8, a newly identified ANGPTL family member by our group that potentiates the inhibitory effect of ANGPTL3 on LPL. .Food intake dramatically up-regulates the expression of ANGPTL8. Whether food intake regulates the cleavage of ANGPTL3 has not been reported. We propose a model that food intake activates ANGPTL3 by two different mechanisms, one is transcriptional regulation of ANGPTL8, and the other is post-transcriptional regulation of the cleavage of ANGPTL3. In the current project, we will first test the hypothesis that food regulates the cleavage of ANGPTL3 post-transcriptionally, and then using cell and animal model to study the upstream signaling pathway. We will also look for the upstream transcription factors and signaling pathway for food induced transcriptional regulation of ANGPTL8. By integrating those two pathways, we hope to fully uncover the mechanisms of food induced activation of ANGPTL3 and pave the ways for drug discovery.

ANGPTL3是肝脏特异分泌性蛋白，主要抑制脂蛋白水解酶LPL的活性，其缺失突变显著降低血脂含量，是当前药物研发的重要靶点。我们前期结果表明，进食活化ANGPTL3，组织特异性的调节LPL活性及甘油三酯的转运。ANGPTL3的活化首先需要一步蛋白酶体切割，切割后的N末端与我们前期发现的另一家族成员ANGPTL8协同作用，调节LPL活性。ANGPTL8的转录表达受进食调节，ANGPTL3切割活化的调控还完全未知。我们猜测，进食一方面增加ANGPTL8的表达，另一方面促进ANGPTL3的切割，协同作用激活ANGPTL3。本项目拟在模式动物中明确不同生理及病理条件下ANGPTL3的切割变化；探讨进食调节ANGPTL3切割的上游信号通路；研究该通路与进食激活ANGPTL8表达通路间的关系；深入揭示进食活化ANGPTL3的分子机制及其在血脂异常发生发展中的作用，为药物研发提供理论依据。

甘油三酯是机体重要的能量来源，血液中的甘油三酯主要以脂蛋白的形式在体内运输循环，通过LPL的水解作用被不同组织吸收利用。耗能器官（心脏、肌肉等）与储存器官（白色脂肪组织）在不同生理病理条件下对甘油三酯的需求不同，这一差异主要通过组织特异性的调节LPL活性来实现。申请人前期工作发现了进食通过增加ANGPTL8的转录表达，进而与ANGPTL3形成复合体，一起从肝脏分泌进入血液，共同抑制进食后耗能器官的LPL活性与甘油三酯摄取，进而促进甘油三酯向储存器官的运输。ANGPTL3在分泌过程中会发生剪切。早期的数据表明切割后的N末端具有更强的抑制LPL的能力， 切割被认为是其活化步骤，但后期的报道又表明N末端与全长ANGPTL3在LPL抑制能力上没有差别，这一剪切的生理意义尚不清楚。本项目中，我们发现小鼠体内Furin家族蛋白是切割Angptl3的关键蛋白酶，并且这一切割过程受Galnt2的糖基化修饰调节。同时我们也制备获得切割缺失的突变体小鼠，初步结果发现其对血脂水平具有显著影响。据此我们发现调节ANGPTL8-ANGPTL3-LPL通路活性的新方式，对理解血脂稳态及血脂异常的发生发展具有重要意义。