铁负荷、铁代谢关键基因多态性及其与HBV感染的交互作用与非酒精性脂肪肝的关系

The development of nonalcoholic fatty liver disease(NAFLD) has been proposed to result from a two-stage process. Firstly, lipid accumulates in the liver, resulting primarily from dietary sources or from the flow of free fatty acids (FFAs) released from adipose tissue. This is frequently associated with IR. The second stage is proposed to result from oxidative stress causing necro-inflammation and cytotoxicity leading to NASH, fibrosis, and ultimately cirrhosis. Iron overload have been implicated in triggering these two stages in vivo and in vitro, indicating that alterations of iron metabolism contributes to the onset of NAFLD and its progression. However, results from epidemiological studies on the association of iron overload with NAFLD remain inconclusive and contradictory. In addition, our preliminary study found that HBV is also associated with NAFLD. However, little is known about whether there is a joint effect between HBV and iron on NAFLD. In this study, we will conduct a case-control study which composed of 1,200 case patients and 1200 age- and sex- frequency matched controls to explore the effects of food intake of iron, plasma iron load, polymorphisms of key genes in iron metabolism and between HBV infection(infection models,HBV genotypes,HBV DNA load and HBV gene mutation) on NAFLD. Multivariable statistical methods will be used to evaluate the potential interactions effects between iron load, gene SNPs and HBV on NAFLD. Our study will not only be helpful for deep understanding of the mechanism involved in NAFLD and finding the risk factors of NAFLD, but also provide scientific evidence for reasonable supplementation of iron in population.

动物和细胞实验均显示铁超载与非酒精性脂肪肝病（NAFLD）发病机制中所涉及的肝脏脂质代谢紊乱、胰岛素抵抗及氧化应激密切相关，而有关铁超载与NAFLD关系的人群流行病学研究却得到矛盾结果。此外，本课题组前期研究发现HBV与肝细胞脂质代谢紊乱及氧化应激有关，可增加NAFLD的患病风险，而铁和HBV在NAFLD发病过程中是否存在联合作用亟待探讨。本项目在前期工作基础上，采用1：1频数匹配病例－对照研究，对膳食铁的摄入量、血清铁负荷相关指标、铁代谢通路中关键基因的多态性（SNPs）及HBV生物学特征（感染模式、基因型、病毒裁量及Pres区突变等）与NAFLD的关系进行研究；运用多因素统计学方法分析铁负荷，SNPs及HBV在NAFLD发生中的主效应和交互作用。本研究结果不仅有助于进一步阐明NAFLD的发病机制和发现NAFLD危险因素，同时也为人群合理地补铁提供科学依据。

随着居民饮食结构和生活方式的变化，我国非酒精性肝病（NAFLD）发病率增长迅速，已成为愈来愈严重的公共卫生问题，且将成为我国卫生经济的巨大负担。本项目应用分子流行病学研究方法，通过比较膳食铁摄入量、血清铁负荷相关指标、铁代谢相关基因多态性及乙型肝炎病毒（HBV）感染在NAFLD组和对照组中的分布差异，探讨HBV感染，铁负荷和铁代谢相关基因多态性（SNP）对NAFLD发病风险的影响。本项目完成了1273例NAFLD新病例和按性别、年龄进行频数匹配的1273例健康对照的流行病学调查及样本收集。现场流行病学调查结果发现膳食血红素铁摄入量增高可增加NAFLD的患病风险，而非血红素铁的摄入量增加则降低NAFLD的患病风险。进一步发现血清ferritin表达增高可增加NAFLD的患病风险，而hepcidin/ferritin 指数增高则降低NAFLD的患病风险。揭示了乙型肝炎病毒（HBV）感染与NAFLD的发病风险密切相关，其作用机制与HBx对FABP1启动子的反式激活作用有关。探讨了6个铁代谢通路关键基因（TFR2，SLC40A1，TFRC，TMPRSS6，BMP6，HFE2等）27个SNPs与NAFLD的关联、及与环境因素间的交互作用。发现TFR2基因rs443445多态性与NAFLD易感性有关,多因素Logistic回归分析提示,携带TFR2基因rs443445突变基因型(GA+GG）可降低NAFLD发病风险，而且rs443445 A／G位点的变异可影响血清ferritin的表达。交互作用分析结果显示，膳食血红素铁摄入增高与超重、高脂摄入、TFR2基因rs443445多态性存在交互作用，但与HBV不存在交互作用。本研究结果对阐明NAFLD发生发展的分子机理、NAFLD易感个体的筛查、NAFLD的早诊及对人群NAFLD的防制都有重要的意义。