ROLE OF SAMe IN LIVER FUNCTION AND INJURY

其在肝功能和损伤中的作用

基本信息

批准号：
7071635
负责人：
Shelly Chi-Loo Lu
金额：
$ 33.74万
依托单位：
UNIVERSITY OF SOUTHERN CALIFORNIA
依托单位国家：
美国
项目类别：
财政年份：
2002
资助国家：
美国
起止时间：
2002-09-20 至 2008-05-31
项目状态：
已结题

项目摘要

DESCRIPTION (provided by applicant): S-adenosylmethionine (SAMe) is vital to normal cell function as the principal biological methyl donor. The enzyme responsible for SAMe biosynthesis is methionine adenosyltransferase (MAT). Of the two genes (MAT1A, MAT2A) that encode MAT, MAT1A is mainly expressed in adult liver. Cirrhotic patients have decreased hepatic MAT 1A mRNA levels and SAMe biosynthesis. Recently we showed the importance of MAT IA in maintaining a normal liver phenotype using the MAT1A null mice. At 3 months, /vIAT1A null mice have reduced hepatic SAMe and GSH levels, hyperplasia, oxidative stress, increased cytochrome P4502E1 (CYP2EI) and uncoupling protein 2 (UCP2) expressions and are prone to liver injury. On a normal diet, MAT1A null mice develop steatohepatitis by 8 months and hepatocellular carcinoma by 18 months. We found that SAMe plays a central role in regulating hepatocyte cell growth and death. SAMe blocks the mitogenic effect of hepatocyte growth factor and inhibits cell cycle progression. SAMe is anti-apoptotic in normal hepatocytes but pro-apoptotic in hepatoma cells. Taken together, our data suggest that normal hepatic SAMe level favors the differentiated state of hepatocytes, blocks apoptosis and prevents cell proliferation. A fall in hepatic SAMe level facilitates liver regeneration but if this condition persists, predisposes to liver injury, steatohepatitis and finally, cancer. This application represents a logical extension of our work and if successfully accomplished, will greatly enhance our understanding of the role of SAMe in liver biology and pathology and its role as a therapeutic agent. The aims are: 1) examine SAMe's effect on cell cycle progression - examine effect on cyclins, cyclin-dependent kinases and their inhibitors in both normal and cancerous hepatocytes; 2) elucidate SAMe's differential effect on apoptosis in normal versus cancerous liver cells - using genomics, proteomics and bioinformatics to identify target genes and proteins that may be responsible; 3) investigate how hepatic SAMe deficiency leads to increased CYP2E1 and UCP2 expression and oxidative stress - examine the molecular mechanism(s) of their induction using MAT1A null mice; 4) examine effects of chronic hepatic SAMe deficiency on CCI4-induced liver fibrosis and SAMe treatment in the absence of MAT1A - examine whether hepatic SAMe deficiency predisposes to fibrosis and whether SAMe's therapeutic effect requires the presence of MATIA; 5) elucidate mechanisms of malignant degeneration in MAT1A knockout mice and possible synergy with p53 knockout - examine the roles of p53 and oval cells as contributing factors to malignant degeneration.

描述（由申请人提供）：S-腺苷甲硫氨酸（SAMe）作为主要的生物甲基供体对于正常细胞功能至关重要。负责 SAMe 生物合成的酶是甲硫氨酸腺苷转移酶 (MAT)。在编码 MAT 的两个基因（MAT1A、MAT2A）中，MAT1A 主要在成人肝脏中表达。肝硬化患者的肝脏 MAT 1A mRNA 水平和 SAMe 生物合成降低。最近，我们使用 MAT1A 缺失小鼠展示了 MAT IA 在维持正常肝脏表型方面的重要性。 3个月时，/vIAT1A缺失小鼠的肝脏SAMe和GSH水平降低、增生、氧化应激、细胞色素P4502E1 (CYP2EI)和解偶联蛋白2 (UCP2)表达增加，并且容易发生肝损伤。在正常饮食下，MAT1A 缺失小鼠在 8 个月时出现脂肪性肝炎，在 18 个月时出现肝细胞癌。我们发现 SAMe 扮演着在调节肝细胞生长和死亡中发挥核心作用。 SAMe 阻断肝细胞生长因子的促有丝分裂作用并抑制细胞周期进程。 SAMe 在正常肝细胞中具有抗凋亡作用，但在肝癌细胞中具有促凋亡作用。综上所述，我们的数据表明正常的肝脏 SAMe 水平有利于肝细胞的分化状态，阻止细胞凋亡并防止细胞增殖。肝脏 SAMe 水平下降有利于肝脏再生，但如果这种情况持续存在，则容易导致肝损伤、脂肪性肝炎，最后导致癌症。该应用代表了我们工作的逻辑延伸，如果成功完成，将极大地增强我们对 SAMe 在肝脏生物学和病理学中的作用及其作为治疗剂的作用的理解。目的是： 1) 检查 SAMe 对细胞周期进展的影响 - 检查对正常和癌性肝细胞中细胞周期蛋白、细胞周期蛋白依赖性激酶及其抑制剂的影响； 2）阐明SAMe对正常肝细胞与癌性肝细胞的凋亡——利用基因组学、蛋白质组学和生物信息学来识别可能负责的靶基因和蛋白质； 3) 研究肝 SAMe 缺陷如何导致 CYP2E1 和 UCP2 表达和氧化应激增加 - 使用 MAT1A 缺失小鼠检查其诱导的分子机制； 4) 检查慢性肝SAMe缺乏对CCI4诱导的肝纤维化和在没有MAT1A的情况下SAMe治疗的影响——检查肝SAMe缺乏是否易导致纤维化以及SAMe的治疗效果是否需要MATIA的存在； 5) 阐明 MAT1A 敲除小鼠的恶性变性机制以及与 p53 敲除可能的协同作用 - 检查 p53 和卵圆细胞作为恶性变性促成因素的作用。