Molecular mechanism of diet-induced carcinogenesis

描述(申请人提供)：近年来，非酒精性脂肪性肝病在西方世界的发病率急剧上升，导致非酒精性脂肪性肝炎(NASH)及其相关并发症(如肝硬变和肝细胞癌)的患病率增加。在美国，NASH正在成为肝癌的主要危险因素，而目前尚无有效的治疗方法。与乙肝病毒/丙型肝炎诱导的肝癌不同，人们对NASH相关肝癌的发病机制(S)知之甚少。我们使用了一种小鼠肝癌模型，在该模型中，服用胆碱缺乏和氨基酸限定(CDAA)饮食的小鼠在22周时发生NASH，在65-75周时发生自发性肝癌的小鼠比例约为75%。此外，这些小鼠表现出明确的病理变化，与人类肝细胞癌的进展明显相似。我们研究的一个关键发现是，在喂养CDAA饮食的早期阶段，与NASH相关的miR-155持续上调，这是一种促炎微RNA。值得注意的是，miR-155在人类NASH和肝细胞癌患者中升高，其水平是肝细胞癌患者不良预后和无复发生存率的独立预测因子。我们假设miR-155在肝细胞和Kupffer细胞(肝脏中的炎性细胞)中上调，在NASH和肝细胞癌中起因果作用。这一建议基于以下新发现：(I)miR-155基因敲除(KO)小鼠在喂养CDAA饮食后4周就表现出炎症和甘油三酯血症的减少，(Ii)泽伦骨(ZER)，一种从食用生姜中提取的倍半萜类植物化学物质，可以抑制小鼠的自发和饮食诱导的炎症反应以及肝癌细胞在培养中的生长，并导致miR-155表达下调。为了验证我们的假设，即操纵miR-155水平和ZER治疗将抑制NASH和肝癌，我们将追求以下三个目标。1(A)利用miR155KO小鼠阐明miR-155在饮食诱导的NASH和肝癌的发生和发展中的作用，以及(B)通过关注miR-155靶点来确定其潜在的机制。2(A)研究在肝细胞或肝细胞+枯否细胞中过表达miR-155的小鼠对饮食诱导的NASH和肝癌的易感性，以及(B)通过鉴定其细胞类型特异性靶点来阐明其差异发病机制。3.通过(A)评估ZER对肝癌细胞的抗致瘤作用，(B)测试其在小鼠体内的抗炎功能，以及(C)阐明其作用的分子基础，探索ZER的预防/治疗潜力。

DESCRIPTION (provided by applicant): The dramatic increase in recent years in the incidence of non-alcoholic fatty liver disease in the Western world has led to an increase in the prevalence of NASH (non-alcoholic steatohepatitis) and associated complications such as cirrhosis and hepatocellular cancer (HCC). In USA, NASH is emerging as a major risk factor for HCC with no effective therapy. Unlike HBV/HCV-induced HCC, very little is known about the mechanism(s) underlying the pathogenesis of NASH-associated HCC. We have used a mouse model of HCC in which 100% mice fed choline-deficient and amino acid defined (CDAA) diet develop NASH by 22 weeks and spontaneous HCC in ~75% mice by 65-75 weeks. Further, these mice exhibit well-defined pathological changes that are markedly similar to the progression of HCC in humans. A key finding from our study is the consistent upregulation of miR-155, a proinflammatory microRNA, from an early stage of feeding CDAA diet that correlates with development of NASH. Notably, miR-155 is elevated in human NASH and HCC patients and its level is an independent predictor of poor prognosis and recurrence-free survival in HCC patients. We hypothesize that upregulation of miR-155 in hepatocytes and Kupffer cells (inflammatory cells in the liver), plays a causal role in NASH and HCCs. This proposal is based on the novel findings that (i) miR-155 knockout (KO) mice exhibit reduced inflammation and triglyceridemia as early as 4 weeks of feeding CDAA diet, and (ii) zerumbone (ZER), a sesquiterpine phytochemical from an edible ginger suppressed both spontaneous and diet-induced inflammatory responses in mice and HCC cell growth in culture and caused downregulation of miR-155. To test our hypothesis that manipulation of miR-155 levels and treatment with ZER will inhibit NASH and HCC, we will pursue the following 3 aims. 1 (a) Elucidate the role of miR-155 in initiation and progression of diet-induced NASH and HCC using miR155KO mice, and (b) identify the underlying mechanism by focusing on miR-155 targets. 2 (a) Investigate the susceptibility of mice overexpressing miR-155 in hepatocytes or in hepatocytes+Kupffer cells to diet induced NASH and HCC, and (b) elucidate the underlying mechanism of differential pathogenesis by identifying its cell type specific targets. 3. Explore preventive/therapeutic potential of ZER by (a) assessing its anti-tumorigenic potential against HCC cells, (b) testing its anti-inflammatory function in mice, and (c) elucidating the molecular basis of its function.