Understanding the regulation of NAD+ homeostasis and signaling

描述（由申请人提供）：烟酰胺腺嘌呤二核苷酸（Nicotinamide adenine dinucleotide, NAD+）是参与多种细胞生化反应的重要辅助因子，参与Ca2+信号传导、染色质结构、DNA修复和寿命的调节。迄今为止，由于NAD+代谢途径的动态性和复杂性，以及难以确定可互转换吡啶核苷酸的水平，调控NAD+稳态的信号通路尚不清楚。烟酰胺核苷（Nicotinamide riboside, NmR）是一种关键的吡啶代谢物，在维持NAD+池和限制热量（CR）诱导的寿命中起重要作用。在本研究中，我们建立了一个核磁共振特异性报告系统，并利用它来鉴定核磁共振/NAD+代谢改变的酵母突变体。我们的初步结果表明，磷酸盐响应信号通路（PHO）参与调控NAD+代谢。我们还发现了NmR/NAD+生物合成和体内平衡途径中的其他新成分。目前的建议建立在我们最近对这些因素的研究基础上，以及NmR/NAD+代谢组分与营养信号通路之间的相互作用。我们研究的长期目标是了解酵母和哺乳动物细胞在应对生长条件变化时维持NAD+稳态的机制。主要的假设是NAD+的稳态是由营养感应信号通路调节的，它在决定细胞的适应性和存活中起着重要的作用。这些项目的具体目标是：目标1)研究营养感应的作用通路在NmR和NAD +体内平衡,目标2)描述一个假定的NmR吸收在NAD +代谢酶,并研究其作用和CR,目标3)研究Fun26守恒的NmR体内平衡因素的角色在NAD +新陈代谢和CR,和目标4)来研究人类的角色Fun26直接同源NAD +体内平衡和CR。实现这些目标,我们将采用分子、遗传和生化方法分析基因,涉及的蛋白质和途径。这些研究将增加我们对真核细胞如何调节NAD+稳态以响应生长条件的变化，以及哪些营养传感信号通路参与其中的理解。我们的发现也有助于理解NAD+体内平衡调控的分子基础，以及与人类NAD+异常代谢相关的代谢紊乱。

DESCRIPTION (provided by applicant): Nicotinamide adenine dinucleotide (NAD+) is an essential cofactor involved in various cellular biochemical reactions and contributes to the regulation of Ca2+ signaling, chromatin structure, DNA repair and lifespan. To date, the signaling pathways that regulate NAD+ homeostasis remain unclear due to the dynamic nature and complexity of the NAD+ metabolic pathways and the difficulty of determining the levels of the interconvertible pyridine nucleotides. Nicotinamide riboside (NmR) is a key pyridine metabolite that plays important roles in the maintenance of NAD+ pool as well as calorie restriction (CR)-induced lifespan. In this proposal, we establish a NmR-specific reporter system and use it to identify yeast mutants with altered NmR/NAD+ metabolism. Our preliminary results show that the phosphate responsive signaling (PHO) pathway contributes to the control of NAD+ metabolism. We have also identified additional novel components in the NmR/NAD+ biosynthesis and homeostasis pathways. The current proposal builds on our recent studies of these factors and the interplay between components in NmR/NAD+ metabolism and the nutrient signaling pathways. The long-term goal of our research is to understand the mechanisms by which yeast and mammalian cells maintain NAD+ homeostasis in response to changes in growth conditions. The major hypothesis is that NAD+ homeostasis is modulated by nutrient-sensing signaling pathway(s), which plays an important role in determining cell fitness and survival. The specific aims of the projects are: Aim 1) To study the role of nutrient sensing pathways in NmR and NAD+ homeostasis, Aim 2) To characterize a putative NmR assimilating enzyme and to study its role in NAD+ metabolism and CR, Aim 3) To study the roles of a conserved NmR homeostasis factor Fun26 in NAD+ metabolism and CR, and Aim 4) To study the role of the human Fun26 orthologs in NAD+ homeostasis and CR. To achieve these goals we will employ a combination of molecular, genetic and biochemical methods to analyze genes, proteins and pathways involved. These studies will increase our understanding of how eukaryotic cells regulate NAD+ homeostasis in response to changes in growth conditions, and which of the nutrient sensing signaling pathways are involved. Our findings may also contribute to the understanding of the molecular basis of the regulation of NAD+ homeostasis as well as metabolic disorders related to aberrant NAD+ metabolism in human.