Integrated molecular epidemiologic analysis of the one-carbon metabolism pathway and risk of HCC

摘要：单碳代谢途径与肝细胞癌的发生发展密切相关。 非酒精性脂肪性肝病(NAFLD)患者的癌症(HCC)。肝癌的发病率有 在美国有所增加，在美国确诊的所有肝细胞癌病例中约有三分之一没有病毒性病毒史 肝炎或酗酒，但这些肝细胞癌病例通常具有NAFLD的临床或生化特征。 事实上，在美国，与非酒精性脂肪肝相关的肝细胞癌病例预计将进一步增加。从功能上讲，一碳 代谢途径通过一碳营养物质的代谢调节DNA甲基化，如胆碱， 蛋氨酸和叶酸，形成S-腺苷蛋氨酸。SAM是用于DNA的通用甲基供体 甲基化；5-甲基胞嘧啶(5mC)的形成。在将甲基从SAM转移到 甲基化，腺苷被转化为S-同型半胱氨酸，它是一种有效的活性抑制剂 DNA甲基转移酶(DNMT)，从而抑制DNA甲基化。因此，在SAM推动 甲基化，SAH抑制甲基化，而SAM/SAH比率反映了一个“肝脏甲基化指数”，因为 SAM和SAH主要形成于肝脏。此外，最近的数据显示，5mC不是静态的 DNA标记，Tet酶将其转化为5-羟甲基胞嘧啶(5HmC)。5hmC现在被认为是 独特的对DNA的表观遗传修饰，不同于5mC。然而，5mC和5hmC都参与了 基因调控和两者都与已建立的肝细胞癌的进展有关，但尚不清楚是哪一种 在这些DNA标记中，与肝细胞癌的发生最相关。这项提议的中心假设是 肝脏甲基化指数或DNA表观遗传修饰的个体差异影响易感性 单独的或与单碳、DNMT或Tet基因的遗传变异一致的肝细胞癌。具体目标是： (1)识别与以下有关的一碳代谢途径中常见和罕见的遗传风险变异 肝细胞癌的风险。(2)评估肝脏甲基化指数(SAM/SAH比值)与肝癌风险的关系。 并确定该关联的单碳基因修饰物。(3)评估表观遗传学与 DNA修饰(5mC和5hmC)与肝癌风险，并通过一碳、DNMT和 TET基因。这项研究的发现有望对单碳代谢产生新的见解 途径作为以前未被认识到的、潜在的可改变的肝细胞癌的贡献者，并改进策略 肝细胞癌的预防、风险分层和早期发现。此应用程序中概述的活动包括 旨在扩大申请人在遗传和分子流行病学方面的专业知识，并获得新的技能 表观遗传学、代谢组学和生物信息学。指导团队的成员具有互补的专业知识 它跨越了这些学科。总体而言，跨学科、综合性的分子流行病学方法 这项提议和职业发展活动，包括正式课程和“动手”讲习班 将使申请人能够获得必要的能力，以促进其向独立的过渡。

ABSTRACT: The one-carbon metabolism pathway is strongly implicated in the development of hepatocellular carcinoma (HCC) in patients with non-alcoholic fatty liver disease (NAFLD). The incidence of HCC has increased in the US, and about a third of all HCC cases diagnosed in the US do not have a history of viral hepatitis or alcohol abuse, but these cases of HCC often have clinical or biochemical features of NAFLD. Indeed, NAFLD-related HCC cases are expected to increase further in the US. Functionally, the one-carbon metabolism pathway regulates DNA methylation through metabolism of one-carbon nutrients, such as choline, methionine and folate, to form S-adenosylmethionine (SAM). SAM is the universal methyl donor used for DNA methylation; the formation of 5-methylcytosine (5mC). Following the transfer of methyl groups from SAM for methylation, SAM is converted to S-adenosylhomocysteine (SAH), which is a potent inhibitor of the activities of DNA methyltransferases (DNMTs) and thus suppresses DNA methylation. Hence, while SAM promotes methylation, SAH inhibits methylation, and the SAM/SAH ratio reflects a “hepatic methylation index” because both SAM and SAH are formed primarily in the liver. Additionally, recent data show that 5mC is not a static DNA mark, it is converted to 5-hydroxymethylcytosine (5hmC) by TET enzymes. 5hmC is now recognized as a unique epigenetic modification to DNA that is distinct from 5mC. However, both 5mC and 5hmC are involved in gene regulation and both have been implicated in the progression of established HCC, but it is unclear which of these DNA marks is most relevant to HCC development. The central hypothesis of this proposal is that individual differences in hepatic methylation index or epigenetic modifications to DNA influence susceptibility to HCC in isolation or in concert with genetic variants in one-carbon, DNMT or TET genes. The Specific Aims are: (1) to identify common and rare genetic risk variants in the one-carbon metabolism pathway associated with HCC risk. (2) To assess the association between hepatic methylation index (SAM/SAH ratio) and HCC risk, and identify one-carbon gene modifiers of the association. (3) To assess the association between epigenetic modifications to DNA (5mC and 5hmC) and HCC risk, and evaluate interaction by one-carbon, DNMT, and TET genes. Findings from this research are expected to yield novel insights into the one-carbon metabolism pathway as a previously under-recognized, potentially modifiable contributor to HCC and improve strategies for the prevention, risk stratification, and early detection of HCC. The activities outlined in this application are designed to extend the applicant’s expertise in genetic and molecular epidemiology, and acquire new skills in epigenetics, metabolomics, and bioinformatics. Members of the mentoring team have complementary expertise that spans these disciplines. Overall, the cross-disciplinary, integrative molecular epidemiologic approach of this proposal and the career development activities that include formal coursework and “hands-on” workshops will enable the applicant to acquire the needed competencies to foster his transition to independence.