Nicotinamide N-methyltransferase is a novel regulator of energy expenditure

描述(由申请人提供)：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方面的新作用。NNMT催化烟酰胺腺嘌呤二核苷酸(NAD+)前体烟酰胺(维生素B3)的S-腺苷蛋氨酸(SAM)甲基化。NNMT是一种独特的酶，因为它同时调节SAM和NAD+这两种细胞能量代谢的基本代谢物。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Sirt1的辅因子，Sirt1是一种脱乙酰酶，调节与能量代谢相关的多个重要靶点。申请人发现，肥胖患者的脂肪组织和肝脏中NNMT水平升高。使用反义寡核苷酸(ASO)从生物上击倒脂肪组织和肝脏中的NNMT可以增加能量消耗，防止饮食诱导的肥胖，并改善胰岛素敏感性。NNMT基因敲除后，脂肪组织中SAM和NAD+水平增加，多胺通量增加，赖氨酸4对H3(H3K4)组蛋白甲基化的单甲基化、双甲基化和三甲基化增强。总体假设是：NNMT是一种新的能量消耗和肥胖调节因子，它通过引起代谢产物分流导致细胞内SAM和NAD+水平的变化来发挥作用，进而调节能量消耗。在目标1中，我们将使用药理学和遗传学的方法来进一步阐明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的活性。对于遗传方法，我们计划产生脂肪特异性的NNMT基因敲除小鼠。我们将调查这些小鼠的能量消耗和肥胖情况。在目标2中，我们将确定SAM改变调节NNMT对能量消耗的影响的机制。我们将重点介绍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+和依赖NAD+的Sirt1是否参与了NNMT调节的能量消耗。该建议在新发现、新机制和综合方法方面具有很高的创新性。它还具有重大的翻译含义。NNMT ASOS和MNA都有可能直接用于临床试验。事实上，MNA已被用于人体研究其血管松弛效应。

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.