Hepatic Nicotinamide N-Methyltransferase (NNMT) as a Pathogenetic Mechanism and Therapeutic Target for Alcoholic Liver Disease

摘要 尽管取得了很大进展，但酒精性肝病（ALD）仍然是世界范围内的主要健康问题。的 疾病过程的特征是早期脂肪变性，脂肪性肝炎，有些人最终 进展为纤维化/肝硬化和肝功能衰竭。不幸的是，目前还没有公认的治疗方法 可以阻止或逆转人类的这一过程。烟酰胺N-甲基转移酶（NNMT）催化 烟酰胺的SAM依赖性降解，烟酰胺是细胞NAD+生物合成的主要前体， 一条救援通道SAM（s-腺苷甲硫氨酸）是甲硫氨酸代谢的第一产物， 细胞转甲基化反应中的通用甲基供体。NNNT在调节两者中的关键作用 NAD+和SAM稳态使其成为一种新兴的新型代谢调节剂。我们是第一个报道 肝脏ATF 4反式激活在介导NNMT上调中起机制作用， 慢性饮酒和腺病毒shRNA敲低NNMT对 酒精性脂肪肝的发展，表明NNMT可以是ALD的理想治疗选择 治疗我们实验室最近获得的初步数据表明，NNMT抑制 与改善的线粒体未折叠蛋白反应（UPRmt）和钝化的肝脏相关。 慢性酒精暴露后的PPAR-gamma激活。在本建议中，我们将进一步阐明 NNMT在ALD发病机制中的作用机制。研究的成功实施 本研究提出的方法不仅为该病的发病机制提供了新的线索， 新的ALD治疗干预方法。这三个目标包括在本提案中， 我们的假设：目的1：描述ALD中NNMT相关肝脏病理的潜在机制。 将进行动物和细胞培养研究，以阐明NNMT抑制的机制。 改善肝脏中的UPRmt诱导，并确定NNMT上调的机制 有助于酒精诱导的肝脏PPAR-gamma激活。目的2：阐明 慢性酒精消耗导致肝ATF 4活化和NNMT上调。两个肝细胞- 特异性Gcn 2敲除小鼠和肝细胞特异性β-内酰胺酶-1过表达小鼠将被喂食 等热量控制或酒精饮食5周。将进行靶向代谢组学， 肝细胞中，以量化酒精对肝精氨酸代谢的影响。目标3：确定两者 NNMT靶向方法对ALD的预防（致病作用）和治疗潜力。动物 肝脏特异性NNMT敲除的小鼠将暴露于等热量控制或酒精饮食。两 将评价NNMT抑制对ALD的预防和治疗功效。

Abstract Despite much progress, alcoholic liver disease (ALD) remains a major health problem worldwide. The disease process is characterized by early steatosis, steatohepatitis, with some individuals ultimately progressing to fibrosis/cirrhosis and liver failure. Unfortunately, there is currently no accepted therapies available to halt or reverse this process in humans. Nicotinamide N-methyltransferase (NNMT) catalyzes SAM-dependent degradation of nicotinamide, a predominant precursor for cellular NAD+ biosynthesis via a salvage pathway. SAM (s-adenosylmethionine) is the first product of methionine metabolism and a universal methyl donor in cellular transmethylation reactions. The critical role of NNNT in regulating both NAD+ and SAM homeostasis make it an emerging novel metabolic regulator. We are the first to report that the liver ATF4 transactivation plays a mechanistic role in mediating NNMT upregulation in the setting of chronic alcohol consumption and adenoviral shRNA knockdown of NNMT is protective against alcoholic fatty liver development, suggesting that NNMT can be an ideal therapeutic choice for ALD treatment. The preliminary data recently obtained from our laboratory uncovered that NNMT inhibition was associated with improved mitochondrial unfolded protein response (UPRmt) and blunted hepatic PPAR-gamma activation upon chronic alcohol exposure. In this proposal, we will further elucidate the mechanistic implication of NNMT in the pathogenesis of ALD. Successful performance of the studies proposed in this proposal will not only shed new light on the pathogenesis of this disease, but also pave the way for novel therapeutic interventions for ALD. The three aims are included in this proposal to test our hypothesis: AIM 1: To delineate mechanism(s) underlying NNMT-associated liver pathologies in ALD. Both animal and cell culture studies will be conducted to elucidate mechanism by which NNMT inhibition improves UPRmt elicitation in the liver and to determine the mechanism whereby NNMT upregulation contributes alcohol-induced liver PPAR-gamma activation. AIM 2: To elucidate mechanism(s) by which chronic alcohol consumption leads to hepatic ATF4 activation and NNMT upregulation. Both hepatocyte- specific Gcn2 knockout mice and hepatocyte-specific arginase-1 overexpressing mice will be fed with isocaloric control or alcohol-diet for 5 weeks. Targeted metabolomics will be conducted to using primary hepatocytes to quantify the effects of alcohol on hepatic arginine metabolism. AIM 3: To determine both preventive (the pathogenic role) and therapeutic potential of NNMT-targeting approach for ALD. Animals with liver-specific NNMT knockout will be exposed to either isocaloric control or alcohol-diet. Both preventive and therapeutic efficacy of NNMT inhibition for ALD will be evaluated.