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

摘要 S-腺苷甲硫氨酸（SAMe）是主要的生物甲基供体，多胺和GSH的前体。肝 在SAMe代谢中起着核心作用，因为这是大部分SAMe作为以下物质的产物产生的地方： 蛋氨酸催化剂该反应由甲硫氨酸腺苷转移酶（MAT）催化。两个基因 编码MAT，MAT 1A在正常分化的肝脏中表达，MAT 2A在所有肝外组织中表达。 组织中在肝脏中，SAMe稳态主要由MAT介导的生物合成和利用控制， 通过甘氨酸N-甲基转移酶（GNMT）完成。我们开发了MAT 1A敲除（KO）小鼠 模型，表现出慢性肝脏SAMe缺乏、氧化应激增加、自发发育 脂肪性肝炎和肝细胞癌（HCC）。这个模型概括了许多病人的情况 慢性肝病，因为肝脏SAMe生物合成受损。我们还开发了GNMT KO小鼠 模型，其中肝SAMe积累到超生理水平，小鼠发生肝损伤、纤维化 还有HCC。该模型与人类疾病有关，因为最近 经鉴定有肝损伤。这些模型在教我们各种功能方面起到了重要作用 SAMe及其在肝脏中调节的途径。这项补助金目前是在其第9年，我们已经出版了 60篇原创论文和22篇评论（42篇原创论文和14篇评论是在过去的资助期内发表的）。在过去 在资助期间，我们发现了SAMe的许多新作用，包括对祖细胞的调节， 群体，肝细胞生长因子介导的信号传导，HuR，LKB 1/AMPK，ERK和AKT活性，组蛋白 翻译后修饰、基因组不稳定性、蛋白质类小泛素化和脂质代谢。我们改进 我们理解当SAMe水平慢性改变时肝损伤如何发生和HCC如何发展。 显然，SAMe不仅仅是一个甲基供体，这笔更新赠款将继续我们的研究， 肝SAMe水平的改变影响肝功能、损伤和癌症发展。三个具体目标是 建议：1.检查SAMe水平的改变如何影响脂质代谢。MAT 1A和GNMT KO小鼠 患上脂肪性肝炎当肝SAMe耗尽时，VLDL组装受损。这一目标将审查 当SAMe过量时脂肪变性是如何发展的。2.检查SAMe如何影响类小泛素化，Myc和 他们的相互作用。在MAT 1A KO小鼠中发生增加的蛋白类小泛素化。我们将阐明机制 并研究它如何与Myc通路相互作用。3.研究SAMe如何影响蛋白质 磷酸化、MAPK和受体酪氨酸激酶（RTK）的活性。我们的初步数据显示 MAPKs和RTK的活性受SAMe的影响。SAMe耗竭有利于磷酸化增加， SAMe处理降低磷酸化。我们将阐明所涉及的机制。成功完成 这些提出的目标将进一步提高我们对改变SAMe代谢如何影响肝功能的认识 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.