Dietary Cancer Prevention in DNA Repair Deficient Mice

描述(申请人提供)：我们细胞中的基因组DNA不断受损并被修复。这种损害是通过暴露在环境遗传毒素中而发生的，例如阳光中的紫外线成分，以及由于内源性代谢产物与DNA发生反应而自发发生的。不修复损伤的后果通过DNA修复途径被扰乱的遗传病来揭示。人类的修复缺陷会导致癌症风险的大幅增加，即使在没有明显接触环境基因毒素的情况下也是如此。因此，癌症的预防有赖于确定内源性DNA损伤的来源以及避免或减弱这种损伤的方法。这些人类修复缺陷综合症的小鼠模型为识别这些来源提供了一个敏感的工具。这项研究的长期目标是使用基因工程缺陷的DNA修复小鼠来识别基因毒性应激的饮食来源和预防癌症的营养干预。ERCC1-XPF是一种核酸内切修复(NER)和修复二价DNA链间交联(ICL)所必需的内切酶。ERCC1-XPF亚型小鼠的实体瘤发生率很高，这不能归因于它们在NER中的缺陷。因此，ERCC1-XPF缺陷小鼠的肿瘤发生可以归因于其ICL修复的缺陷，从而导致自发性ICL的结果。我们假设，在这种DNA修复缺陷模型中，促进自发性肿瘤的ICL损伤是由脂质过氧化(LPO)引起的。提出的实验将通过用富含促进内源性LPO的多不饱和脂肪酸的饮食来挑战ERCC1-XPF亚型小鼠来验证这一假设。该项目的具体目标是确定饮食中的多不饱和脂肪酸(PUFA)是否会促进癌症。饮食中的多不饱和脂肪酸同化进入细胞膜，特别容易被氧化，从而增加体内的脂质过氧化(LPO)。膜多不饱和脂肪酸的LPO产生能够使DNA交联的醛。我们假设LPO是自发ICL的来源，有助于修复缺陷小鼠的肿瘤发生。通过饲喂富含多不饱和脂肪酸的饲料，可诱导ERCC1-XPF亚型小鼠发生LPO。第二组动物将接受不含多不饱和脂肪酸的等卡路里饮食。我们预测，喂食富含多不饱和脂肪酸饮食的动物将有更高的发病率和/或更早的实体肿瘤发病。这些实验的结果将表明，饮食脂肪是否会增加内源性DNA损伤的数量，以及这种损伤是否可以促进肿瘤的发生。同样，研究结果将揭示，避免饮食中的多不饱和脂肪酸是否会降低癌症风险。最后，这些实验将揭示ERCC1-XPF亚型小鼠是否是筛选可能降低癌症风险的抗氧化剂的有用模型。

DESCRIPTION (provided by applicant): The genomic DNA in our cells is continuously damaged and repaired. The damage occurs via exposure to environmental genotoxins such as the UV component of sunlight and spontaneously due to endogenous metabolites that react with DNA. The consequences of not repairing the damage are revealed by genetic diseases in which DNA repair pathways are disrupted. Repair deficiency in humans can lead to a profound increase in the risk of cancer, even in the absence of obvious exposure to environmental genotoxins. Thus prevention of cancer is dependent upon identifying the sources of endogenous DNA damage and means to avoid or attenuate it. Mouse models of these human repair deficiency syndromes offer a sensitive tool for identifying these sources. The long term objective of this research is to use mice, genetically engineered to be deficient in DNA repair to identifying dietary sources of genotoxic stress and nutritional interventions that prevent cancer. ERCC1-XPF is an endonuclease required for nucleotide excision repair (NER) of bulky lesions on one strand of DNA and the repair of bivalent DNA interstrand crosslinks (ICL). Mice hypomorphic for ERCC1-XPF have a very high incidence of solid tumors, which cannot be attributed to their defect in NER. Thus tumorigenesis in ERCC1-XPF-deficient mice can be attributed to their defect in ICL repair, and therefore the consequence of spontaneous ICL. We hypothesize that the ICL damage that promotes spontaneous tumors in this DNA repair-deficient model is caused by lipid peroxidation (LPO). Experiments proposed will test this hypothesis by challenging the ERCC1-XPF hypomorphic mice with a diet rich in polyunsaturated fatty acids, which promote endogenous LPO. The specific aim of this project is to determine if dietary polyunsaturated fatty acids (PUFA) promote cancer. Dietary PUFA assimilate into cell membranes and are particularly vulnerable to oxidation, thus increase lipid peroxidation (LPO) in vivo. LPO of membrane PUFA produces aldehydes able to crosslink DNA. We hypothesize that LPO is a source of spontaneous ICL that contribute to tumorigenesis in the repair-deficient mice. LPO will be induced in ERCC1-XPF hypomorphic mice by administering a diet rich in PUFA. A second cohort of animals will receive an isocaloric diet depleted of PUFA. We predict that animals fed the PUFA-rich diet will have an increased incidence and/or earlier onset of solid tumors. The results from these experiments will indicate if dietary fats increase the amount of endogenous DNA damage and if this damage can promote tumorigenesis. Similarly, the results will reveal if avoiding dietary PUFA reduces cancer risk. Finally, these experiments will reveal if ERCC1-XPF hypomorphic mice are a useful model for screening anti-oxidants that may reduce cancer risk.