Nicotinamide N-methyltransferase is a novel regulator of energy expenditure

描述（由申请方提供）：当前提案的总体目标是研究烟酰胺N-甲基转移酶（NNMT）在调节能量消耗和肥胖中的新作用。NNMT催化烟酰胺（维生素B3）（烟酰胺腺嘌呤二核苷酸（NAD+）的前体）的S-腺苷甲硫氨酸（SAM）依赖性甲基化。NNMT是一种独特的酶，因为它调节细胞能量代谢的两种基本代谢物SAM和NAD+。SAM为多胺代谢提供底物丙胺，并为组蛋白甲基化提供甲基。多胺代谢和组蛋白甲基化都参与调节能量消耗。NAD+是Sirt 1的辅因子，Sirt 1是一种去乙酰化酶，调节与能量代谢相关的多个重要靶点。申请方发现NNMT在肥胖症患者的脂肪组织和肝脏中升高。使用反义寡核苷酸（阿索）生物敲除脂肪组织和肝脏中的NNMT增加能量消耗，防止饮食诱导的肥胖并改善胰岛素敏感性。NNMT敲低增加SAM和NAD+水平，增强多胺通量，并增强脂肪组织中H3（H3 K4）组蛋白甲基化上赖氨酸4的单甲基化、二甲基化和三甲基化。总体假设是：NNMT是一种新型的能量消耗和肥胖调节剂，它通过引起代谢物分流导致细胞SAM和NAD+水平的变化来发挥其作用，从而调节能量消耗。在目标1中，我们将使用药理学和遗传学方法来进一步阐明NNMT在调节能量消耗中的作用。对于药理学方法，我们将使用N-甲基烟酰胺（MNA），一种NNMT反馈抑制剂，来抑制NNMT活性。对于遗传方法，我们计划产生脂肪特异性NNMT敲除小鼠。我们将研究这些小鼠的能量消耗和肥胖。在目标2中，我们将确定SAM的改变介导NNMT对能量消耗的影响的机制。我们将集中在SAM调节的多胺代谢和组蛋白甲基化。在目标3中，我们将研究NAD+和NAD+依赖性Sirt 1是否参与NNMT调节的能量消耗。该方案在新发现、新机制和综合方法等方面具有很强的创新性。它还具有重要的翻译意义。NNMT ASO和MNA都有可能直接用于临床试验。事实上，MNA已被用于人类研究其血管舒张作用。

DESCRIPTION (provided by applicant): The overall goal of the current proposal is to investigate the novel roles of nicotinamide N- methyltransferase (NNMT) in regulating energy expenditure and adiposity. NNMT catalyzes the S- adenosylmethionine (SAM)-dependent methylation of nicotinamide (vitamin B3), a precursor of nicotinamide adenine dinucleotide (NAD+). NNMT is a unique enzyme in that it regulates both SAM and NAD+, two fundamental metabolites for cellular energy metabolism. SAM provides substrate propylamine for polyamine metabolism and donates a methyl group for histone methylation. Both polyamine metabolism and histone methylation are involved in regulating energy expenditure. NAD+ is a cofactor of Sirt1, a deacetylase that regulates multiple important targets related to energy metabolism. The applicant found that NNMT was elevated in adipose tissue and liver in obesity. Biologically knocking down NNMT in adipose tissue and liver using antisense oligonucleotides (ASO) increased energy expenditure, prevented diet-induced obesity and improved insulin sensitivity. NNMT knockdown increased SAM and NAD+ levels, enhanced polyamine flux and augmented mono-, di- and tri-methylation of lysine 4 on H3 (H3K4) histone methylation in adipose tissue. The overall hypothesis is: NNMT is a novel regulator of energy expenditure and adiposity, and it exerts its effects by causing metabolite shunting leading to changes in cellular SAM and NAD+ levels, which in turn regulate energy expenditure. In Aim 1, we will use pharmacological and genetic approaches to further elucidate the roles of NNMT in regulating energy expenditure. For pharmacological approach, we will use N-methylnicotinamide (MNA), an NNMT feedback inhibitor, to inhibit NNMT activity. For genetic approach, we plan to generate adipose-specific NNMT knockout mice. We will investigate energy expenditure and adiposity in these mice. In Aim 2, we will determine the mechanisms by which alterations in SAM mediate the effects of NNMT on energy expenditure. We will focus on SAM-regulated polyamine metabolism and histone methylation. In Aim 3, we will investigate whether NAD+ and NAD+-dependent Sirt1 are involved in NNMT-regulated energy expenditure. The proposal is highly innovative in the aspects of new discovery, novel mechanisms and comprehensive approaches. It also has significant translational implications. Both NNMT ASOs and MNA can potentially be used directly in clinical trials. In fact, MNA has been used in humans for studying its vasorelaxation effects.