Role of SAMe in Pathogenesis and Treatment of Non-Alcholic Fatty Liver Disease

摘要 S-腺苷蛋氨酸(SAME)是主要的生物甲基供体，是多胺和谷胱甘肽的前体。肝 在相同的新陈代谢中起核心作用，因为这是产生相同的大部分相同的产品 蛋氨酸分解代谢。该反应由蛋氨酸腺苷转移酶(MAT)催化。两个基因 编码MAT，MAT1A在正常分化的肝脏中表达，MAT2A在所有肝外表达 纸巾。在肝脏中，相同的动态平衡主要由MAT介导的生物合成和利用控制，很大程度上 由甘氨酸N-甲基转移酶(GNMT)完成。我们开发了MAT1A基因敲除(KO)小鼠 模型表现为慢性肝同虚，氧化应激增加，自发发育 脂肪性肝炎和肝细胞癌。这个模型概括了许多患者的情况。 与肝脏一样的慢性肝病，同样的生物合成也受到损害。我们还开发了GNMT KO小鼠 模型中，肝组织中的丙二醛积聚到超生理水平，小鼠出现肝损伤、纤维化 还有肝细胞癌。这种模式与人类疾病有关，因为最近发生了GNMT突变的儿童 被确认为肝脏受损。这些模型在教授我们各种功能方面起到了很大作用 以及它在肝脏中调节的途径。这笔赠款目前已进入第9个年头，我们已经发布了 60篇原创论文和22篇评论(42篇原创论文和14篇评论，在过去的资助期内)。在过去 在资助期间，我们发现了许多相同的新行为，包括对祖细胞的调节 群体，肝细胞生长因子介导的信号转导，HUR，LKB1/AMPK，ERK和AKT活性，组蛋白 翻译后修饰、基因组不稳定、蛋白质相加和脂类代谢。我们改进了 当同一水平发生慢性改变时，我们对肝损伤发生和肝细胞癌发生的理解。 显然，同样的不仅仅是甲基捐赠者，这笔续期赠款将继续我们对如何 肝脏同型半胱氨酸水平的改变会影响肝功能、损伤和肿瘤的发生。三个具体目标是 建议：1.检查相同水平的改变如何影响脂肪代谢。Mat1a和GNMT KO小鼠 患上脂肪性肝炎。当肝脏中的极低密度脂蛋白被耗尽时，极低密度脂蛋白的组装就会受到损害。这一目标将检验 当同样的过量发生时，脂肪变性是如何发展的。2.研究SIME如何影响相扑、Myc和 它们之间的相互作用。在MAT1AKO小鼠中，蛋白质相加甲基化增加。我们将阐明其机制(S) 并研究其与Myc通路的相互作用。3.研究它们对蛋白质的影响 磷酸化、MAPKs活性和受体酪氨酸激酶(RTKs)。我们的初步数据显示 MAPK和RTK的活性也受其影响。同样的消耗有利于增加磷酸化，而 同样的处理会降低磷酸化水平。我们将阐明其中涉及的机制。成功完成 这些建议的目标将进一步加强我们对改变的相同代谢如何影响肝功能的了解。 并帮助确定将从其治疗用途中受益的患者，这与公共卫生高度相关。

ABSTRACT S-adenosylmethionine (SAMe) is the principal biological methyl donor, precursor of polyamines and GSH. Liver plays a central role in SAMe metabolism, as this is where the bulk of SAMe is generated as the product of methionine catabolism. This reaction is catalyzed by methionine adenosyltransferase (MAT). Two genes encode for MAT, MAT1A is expressed in normal differentiated liver and MAT2A is expressed in all extrahepatic tissues. In liver, SAMe homeostasis is controlled by MAT-mediated biosynthesis and utilization, largely accomplished by glycine N-methyltransferase (GNMT). We developed the MAT1A knockout (KO) mouse model, which exhibits chronic hepatic SAMe deficiency, increased oxidative stress, spontaneous development of steatohepatitis and hepatocellular carcinoma (HCC). This model recapitulates the situation in many patients with chronic liver disease as hepatic SAMe biosynthesis is impaired. We also developed the GNMT KO mouse model, where hepatic SAMe accumulates to supraphysiological level and the mice develop liver injury, fibrosis and also HCC. This model is relevant to human disease as children with GNMT mutations were recently identified to have liver injury. These models have been instrumental in teaching us about the various functions of SAMe and pathways that it regulates in the liver. This grant is currently in its 9th year and we have published 60 original papers plus 22 reviews (42 original and 14 reviews in the past funding period). During the past funding period we uncovered numerous novel actions of SAMe that include regulation of progenitor cell population, hepatocyte growth factor-mediated signaling, HuR, LKB1/AMPK, ERK, and AKT activities, histone post-translational modifications, genomic instability, protein sumoylation, and lipid metabolism. We improved our understanding of how liver injury occurs and HCC develops when SAMe level is chronically altered. Clearly, SAMe is much more than just a methyl donor and this renewal grant will continue our study on how alteration of hepatic SAMe level affects liver function, injury and cancer development. Three specific aims are proposed: 1. Examine how altered SAMe levels affect lipid metabolism. Both MAT1A and GNMT KO mice develop steatohepatitis. VLDL assembly is impaired when hepatic SAMe is depleted. This aim will examine how steatosis develops when SAMe excess occurs. 2. Examine how SAMe affects sumoylation, Myc and their interplay. Increased protein sumoylation occurs in MAT1A KO mice. We will elucidate the mechanism(s) involved and examine how this interacts with the Myc pathway. 3. Examine how SAMe affects protein phosphorylation, activity of MAPKs and receptor tyrosine kinases (RTKs). Our preliminary data indicate activity of MAPKs and RTKs are affected by SAMe. SAMe depletion favors increased phosphorylation while SAMe treatment lowers phosphorylation. We will elucidate the mechanisms involved. Successful completion of these proposed aims will further enhance our knowledge of how altered SAMe metabolism affects liver function and help to identify patients that will benefit from its therapeutic use, which are highly relevant to public health.