Mechanisms in Metabolic Control in C. elegans.

描述(申请人提供)：生命依赖于食物到能量的转化。然而，食物摄入的不平衡、遗传变异或环境因素可能会改变代谢途径，导致2型糖尿病、脂肪肝、代谢综合征或心血管疾病。在这样一个复杂的系统中，很难确定原因和结果；因此，重要的是确定可能影响多个代谢终点的共同调节点。SREBP(固醇调节结合元件蛋白)家族的转录因子协调脂肪酸、胆固醇和磷脂生物合成所需基因的激活(Horton，2002)。他们还通过表达乙酰辅酶A和NADPH合成基因来确保这些生物合成途径有足够的构建块。我们发现，SREBPs对于产生与这些过程相关的另一种代谢物：S-腺苷蛋氨酸(SAME)是重要的。相同的是由一个碳循环(1cc)产生的，是磷脂生物合成和表观遗传修饰以及其他细胞过程所必需的。越来越多的证据表明1cc功能与脂肪肝疾病和肝癌的发生有关(Mato，2008)。我们的研究发现SREBPs影响这一途径中的关键基因的表达，这表明脂质平衡和1cc代谢物如蛋氨酸、同型半胱氨酸等水平可能受到协调调节。在这项建议中，我们将结合对线虫的研究，这是一种具有保守脂质生物学的无脊椎动物模型，并结合哺乳动物细胞培养系统的机制分析，以确定1cc的哪些方面对SREBP在体内的功能是必不可少的。我们将研究引导脂肪酸生物合成基因SREBP激活的信号是否也影响1cc基因。对1CC中SREBP靶点的表型分析表明，SAMS-1(S-腺苷蛋氨酸合成酶)基因敲除会导致大脂滴的形成。这些液滴使人想起当以小鼠同源基因(MAT1A)为靶点时出现的肝脏脂肪变性(Mato，2008)，并表明线虫可能模拟脂肪性肝病中脂肪积累的各个方面。线虫能够通过RNAi、代谢谱和饮食操作快速失活基因，为剖析SREBP和1cc代谢之间的调节相互作用提供了一个很好的模型，这种相互作用可以在更复杂的哺乳动物模型中扩展。这项提案中的实验将影响我们对营养、新陈代谢和疾病之间联系的轻描淡写。

DESCRIPTION (provided by applicant): Life depends upon the conversion of food to energy. However, imbalances in food intake, genetic variations or environmental factors can alter metabolic pathways, causing type 2 diabetes, fatty liver disease, metabolic syndrome or cardiovascular disease. Determining causes and effects in such a complex system is difficult; therefore it is important to identify common regulatory points that may impact multiple metabolic endpoints. Transcription factors from the SREBP (sterol regulatory binding element protein) family coordinate activation of genes necessary for fatty acid, cholesterol and phospholipid biosynthesis (Horton, 2002). They also insure these biosynthetic pathways have adequate building blocks by expressing Acetyl CoA and NADPH synthesis genes. We have found that SREBPs are important for generating another metabolite linked to these processes: s-adenosyl methionine (SAMe). SAMe is produced by the one carbon cycle (1CC) and necessary for phospholipid biosynthesis and epigenetic modification in addition to other cellular processes. A growing body of evidence has linked 1CC function with fatty liver disease and the development of liver cancer (Mato, 2008). Our finding that SREBPs affect expression of key genes in this pathway suggests lipid homeostasis and levels of 1CC metabolites such as methionine, homocysteine, and SAMe may be coordinately regulated. In this proposal, we will combine studies in C. elegans, an invertebrate model with conserved lipid biology, with mechanistic analysis in mammalian cell culture systems to determine which aspects of 1CC are essential for SREBP function in vivo. We will examine if signals directing SREBP activation of fatty acid biosynthesis genes also affect 1CC genes. Phenotypic analysis of a SREBP target in the 1CC has revealed that sams-1 (s-adenosyl methionine syntase) knockdown causes formation of large lipid droplets. These droplets are reminiscent of the hepatic steatosis appearing when the mouse ortholog (MAT1A) is targeted (Mato, 2008) and suggest C. elegans may model aspects of the lipid accumulation in fatty liver disease. C. elegans are amenable to rapid gene inactivation by RNAi, metabolic profiling and dietary manipulation, providing an excellent model for dissecting the regulatory interactions between SREBP and 1CC metabolism which can be expanded in more complex mammalian models. The experiments in this proposal will impact our understating of links between nutrition, metabolism and disease.