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

摘要：一碳代谢途径与肝细胞的发育密切相关 非酒精性脂肪肝（NAFLD）患者的肝癌（HCC）。肝癌的发病率 在美国增加，在美国诊断的所有HCC病例中约有三分之一没有病毒感染史。 肝炎或酗酒，但这些HCC病例通常具有NAFLD的临床或生化特征。 事实上，NAFLD相关的HCC病例预计将在美国进一步增加。从功能上讲，一碳 代谢途径通过代谢一碳营养物，如胆碱， 甲硫氨酸和叶酸，以形成S-腺苷甲硫氨酸（SAM）。SAM是DNA的通用甲基供体 甲基化; 5-甲基胞嘧啶（5 mC）的形成。在从SAM转移甲基之后， 甲基化后，SAM转化为S-腺苷高半胱氨酸（SAH），这是一种有效的抑制剂， DNA甲基转移酶（DNMT），从而抑制DNA甲基化。因此，虽然SAM促进 SAH抑制甲基化，SAM/SAH比率反映“肝甲基化指数”，因为 SAM和SAH都主要在肝脏中形成。此外，最近的数据表明，5 mC不是静态的， DNA标记，通过泰特酶转化为5-羟甲基胞嘧啶（5 hmC）。5 hmC现在被认为是 对DNA的独特表观遗传修饰，与5 mC不同。然而，5 mC和5 hmC都参与了 基因调控和两者都与已建立的HCC的进展有关，但尚不清楚是哪一种 这些DNA标记中的一个与HCC的发展最相关。这一提议的核心假设是， 肝甲基化指数或DNA表观遗传修饰的个体差异影响对 HCC单独存在或与一碳、DNMT或泰特基因的遗传变异相关。具体目标是： (1)确定与以下疾病相关的一碳代谢途径中常见和罕见的遗传风险变异： HCC风险。(2)为了评估肝甲基化指数（SAM/SAH比值）与HCC风险之间的关系， 并鉴定该关联的一碳基因修饰物。(3)为了评估表观遗传学与 DNA修饰（5 mC和5 hmC）和HCC风险，并通过一碳，DNMT和 泰特基因。这项研究的结果有望为单碳代谢提供新的见解 作为一个以前认识不足的，潜在的可改变的HCC的贡献者，并改善策略， HCC的预防、危险分层和早期发现。本申请中概述的活动包括 旨在扩展申请人在遗传和分子流行病学方面的专业知识，并获得以下方面的新技能： 表观遗传学、代谢组学和生物信息学。指导小组成员具有互补的专业知识 跨越这些学科。总体而言，跨学科，综合分子流行病学的方法， 这一建议和职业发展活动，包括正式的课程和“动手”讲习班 将使申请人获得必要的能力，以促进其向独立过渡。

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.