Mechanisms in Metabolic Control in C. elegans.

描述（由申请人提供）：生命取决于食物转化为能量。然而，食物摄入的不平衡，遗传变异或环境因素可以改变代谢途径，导致2型糖尿病，脂肪肝疾病，代谢综合征或心血管疾病。在这样一个复杂的系统中确定原因和影响是困难的;因此，重要的是要确定可能影响多个代谢终点的共同调控点。来自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必需的基因的活化（Horton，2002）。它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具有足够的构建模块。我们发现SREBP对于产生与这些过程相关的另一种代谢物：S-腺苷甲硫氨酸（SAMe）非常重要。SAMe是由一个碳循环（1CC）产生的，除了其他细胞过程外，还为磷脂生物合成和表观遗传修饰所必需。越来越多的证据表明，1CC功能与脂肪肝和肝癌的发展有关（Mato，2008）。我们发现SREBPs影响该途径中关键基因的表达，这表明脂质稳态和1CC代谢产物（如蛋氨酸、同型半胱氨酸和SAMe）的水平可能受到协调调节。 在这个建议中，我们将联合收割机的研究在C。elegans，一种具有保守脂质生物学的无脊椎动物模型，在哺乳动物细胞培养系统中进行机制分析，以确定1CC的哪些方面对体内SREBP功能至关重要。我们将研究是否信号指导SREBP激活脂肪酸生物合成基因也影响1CC基因。对1CC中SREBP靶标的表型分析表明，sams-1（s-腺苷甲硫氨酸合成酶）敲低导致形成大脂滴。这些液滴使人联想到当靶向小鼠直系同源物（MAT 1A）时出现的肝脂肪变性（Mato，2008），并提示C.秀丽隐杆线虫可以模拟脂肪肝疾病中脂质积累的各个方面。C.线虫易于通过RNAi、代谢谱分析和饮食操纵进行快速基因失活，这为剖析SREBP和1CC代谢之间的调节相互作用提供了极好的模型，该模型可以在更复杂的哺乳动物模型中扩展。本提案中的实验将影响我们对营养、代谢和疾病之间联系的理解。 公共卫生相关性：脂肪肝、2型糖尿病和心血管疾病的特征是代谢功能障碍，但很难确定营养和遗传因素如何影响疾病进展。在我们的建议中的研究利用一个简单的无脊椎动物模型，C。elegans，以发现脂质生产和一个碳循环代谢物，如s-腺苷甲硫氨酸和同型半胱氨酸之间的联系，并扩大这一分析哺乳动物系统。这项研究将（1）提高我们对人类疾病中至关重要的代谢途径如何协调调节的理解，（2）扩大我们对营养，遗传学和疾病之间联系的了解。

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. PUBLIC HEALTH RELEVANCE: Fatty liver disease, type 2 diabetes and cardiovascular disease are characterized by metabolic dysfunction, yet it is difficult to determine how nutritional and genetic factors impact disease progression. The studies in our proposal utilize a simple invertebrate model, C. elegans, to discover links between lipid production and one carbon cycle metabolites such as s-adenosyl methionine and homocysteine and to expand this analysis to mammalian systems. This research will (1) enhance our understanding of how metabolic pathways, critical in human disease, are coordinately regulated and (2) expand our knowledge of the links between nutrition, genetics and disease.