SREBPs in Regulation of Lipid Metabolism

描述（申请人提供）：我们的研究方向是营养输入和代谢需求调控脂质代谢基因的机制。在哺乳动物中，有三种SREBPs是脂质代谢基因的主要调节因子。SREBP-1a和1c由来自单个基因的重叠mrna编码，而SREBP-2由不同的基因转录。SREBPs通过其bHLHLZ结构域将DMA作为二聚体结合，并且它们具有相互同源和异源二聚的潜力。在本研究中，我们通过结合细胞培养和动物模型来评估个体同源和异源二聚体在激活SREBP靶基因中的具体功能，以获得这些复杂转录因子对脂质调节的多层次视角。在Aim 1中，我们设计了同时表达两种不同SREBP同种异构体的转化细胞（每一种都在单独的调节诱导剂的控制下），以检查单个SREBP同属和异源二聚体在结合和激活靶基因中的功能作用。在Aim 2中，我们不再对单个SREBP进行人工操纵，而是在小鼠模型中关注饮食波动和药理学挑战对SREBP结合和靶基因激活的影响。在Aim 3中，我们结合了人工操作SREBPs和动物模型的优势，研究了同时过表达1a和1c的小鼠。这是特别有趣的，因为它将允许我们在动物模型中测试1c减弱1a活性的假设（基于细胞培养研究）。这些研究具有重要意义，原因有二：1)了解单个SREBPs的功能将预测其表达的生理或药理学变化如何改变动物的脂质代谢；2)人类基因组仅包含30,000个个体基因，因此基因数量不足以解释个体人类难以置信的复杂性。来自重叠mrna的多种蛋白质的表达（如SREBP-1a和-1c）和蛋白质单体的差异结合成具有独特功能特性的不同二聚体/复合物（也是srebp的特性）是显着增加基因组编码潜力的两种机制。因此，SREBP系统提供了一个定义良好的实验模型来评估促进基因组复杂性从DNA水平扩展到蛋白质水平的分子机制。

DESCRIPTION (provided by applicant): Our research program is focused on mechanisms by which nutritional input and metabolic demand regulate genes of lipid metabolism. In mammals there are three SREBPs that are major regulators of genes in lipid metabolism. SREBP-1a and 1c are encoded by overlapping mRNAs from a single gene and SREBP-2 is transcribed from a distinct gene. SREBPs bind DMA as dimers through their bHLHLZ domains and they have the potential to homo and heterodimerize with one another. In this proposal, we evaluate the specific functions of the individual homo and heterodimers in activation of SREBP target genes by combining cell culture and animal models to obtain a multi-level perspective on lipid regulation by these complex transcription factors. In Aim 1 we engineer transformed cells that simultaneously express only two different SREBP isoforms (each under the control of a separate regulatory inducer) in order to examine the functional roles of the individual SREBP homo and heterodimers in binding to and activation of target genes. In Aim 2 we move away from artificial manipulation of the individual SREBPs and instead focus on the consequences of dietary fluctuation and pharmacologic challenge to SREBP binding and activation of target genes in a mouse model. In Aim 3 we combine the strengths of artificial manipulation of SREBPs and animal models to study mice that over-express both 1a and 1c simultaneously. This is of particular interest because it will allow us to test our hypothesis that 1c attenuates 1 a activity (based on cell culture studies) in an animal model. These studies are highly significant for two reasons: 1) understanding the function of the individual SREBPs will predict how physiologic or pharmacologic changes in their expression alter lipid metabolism in animals, 2) The human genome contains only 30,000 individual genes, so gene number is insufficient to account for the incredible complexity of an individual human being. Expression of multiple proteins from overlapping mRNAs (like SREBP-1a and -1c) and differential association of protein monomers into distinct dimers/complexes with unique functional properties (also a property of SREBPs) are two mechanisms that significantly increase genomic coding potential. Thus, the SREBP system provides a well-defined experimental model to evaluate molecular mechanisms that contribute to the expansion of genome complexity from the DNA to protein level.