The contribution of DNA interstrand crosslinks to aging

描述(由申请人提供)： 衰老的特征是功能储备的丧失，使老年人患多种疾病的风险增加。找出这种功能丧失背后的驱动力，对于维持健康的人群至关重要。来自我们实验室和其他实验室的最新证据表明，DNA损伤是衰老的原因之一。这意味着环境因素对衰老有很强的影响。这项研究的长期目标是了解DNA损伤促进衰老的分子机制。这一点，再加上确定遗传毒性应激的环境原因，将极大地促进预防与年龄相关的疾病。ERCC1-XPF是一种内切酶，通过核苷酸切除修复(NER)和DNA链间交联(ICL)，通过一种不同的机制修复庞大的单加合物。小鼠中ERCC1-XPF的缺失会导致早期衰老。因此，这些小鼠提供了一个独特、快速和灵敏的模型系统，用于发现哪些基因毒素促进衰老以及它们是如何促进衰老的。ErcCL小鼠的表型不能归因于NER的丢失。因此，我们的工作假设是，ERCC1-XPF缺陷小鼠的快速衰老是由于它们无法修复ICL，因此是内源性ICL具有细胞毒性的结果。为了测试这一点，研究人员设计了ERCC1-XPF的下构型小鼠，这些小鼠在几个月的过程中老化，允许进行干预性研究。这些小鼠将暴露在促进脂质过氧化(LPO)的DNA交联药物和环境制剂中，LPO可能是内源性ICL的来源，以确定这些暴露是否会加剧小鼠的黄体症状。研究人员发现了一种由XPF突变引起的人类早衰症。因此，确定ERCC1-XPF基因缺陷小鼠快速衰老的原因将直接影响人类健康。本项目的具体目标是：目的I：确定ERCC1-XPF缺陷细胞对DNA、ICLS和LPO的细胞反应。ERCC1-XPF缺陷细胞将暴露在8-MOP或当归素类植物来源的补骨脂素中。光激活8-MOP可诱导ICL和单加合物，而当归素光活化只产生单加合物。将测量细胞存活率、细胞衰老、细胞凋亡率、突变频率和染色体畸变率。如果我们的假设是正确的，那么在诱导相同数量的DNA损伤的条件下，8-MOP的细胞毒性将明显高于当归素类。ERCCl-XPF缺陷细胞还将暴露在镉中，镉是一种促进LPO的环境因素，以确定LPO是否引起与ICL相同的细胞反应。目的II：直接检验未修复的DNA ICL促进衰老的假说。ERCC1-XPF亚型小鼠将长期暴露于交联剂机械氯乙胺。第二个队列将暴露于2-氯乙胺(它会诱导结构上相关的单加合物，但不会导致ICL)，剂量与机械氯乙胺诱发相同数量的病变。如果我们的假设是正确的，机械氯乙胺，而不是2-氯乙胺，会加剧这些小鼠的衰老。结果将通过比较外用8-MOP和当归素加UV-A对仅在皮肤中存在ERCC1-XPF基因缺失的小鼠的皮肤老化反应来证实。目的III：确定脂质过氧化(LPO)是否促进ICL修复缺陷小鼠的衰老。LPO是由氧自由基对细胞膜的破坏引起的，并产生能够使DNA交联的产物。我们假设LPO是导致ERCCL小鼠表型的ICL的来源之一。在ERCC1-XPF缺陷小鼠中，通过接触CCl4或镉可诱导LPO。如果我们的假设是正确的，与野生型小鼠相比，ErcCL小鼠将对LPO过敏，LPO将加剧它们的衰老。这些实验的结果将表明LPO是否促进衰老，如果是，它是否通过诱导DNA损伤来促进衰老。这些实验还将揭示两种常见的工业暴露是否会促进衰老。

DESCRIPTION (provided by applicant): Aging is characterized by loss of functional reserve, placing the elderly at increased risk of numerous diseases. Identifying the driving force behind this functional loss is essential for maintaining a healthy populace. Recent evidence from our lab and others implicates DNA damage as a cause of aging. This implies a strong environmental component to aging. The long term objective of this research is to understand the molecular mechanism by which DNA damage promotes aging. This coupled with identifying environmental causes of genotoxic stress will greatly facilitate prevention of age-associated diseases. ERCC1-XPF is an endonuclease required for repair of bulky monoadducts via nucleotide excision repair (NER) and DNA interstrand crosslinks (ICLs) via a distinct mechanism. Deletion of ERCC1-XPF in the mouse causes early onset aging. These mice therefore offer a unique, rapid and sensitive model system for discovering which genotoxins promote aging and how they do so. The phenotype of the Erccl mice cannot be attributed to loss of NER. Thus our working hypothesis is that rapid aging in ERCC1-XPF deficient mice is caused by their inability to repair ICLs and therefore a consequence of endogenous ICLs which are cytotoxic. To test this, the investigators engineered mice hypomorphic for ERCC1-XPF which age over the course of months, permitting interventional studies. These mice will be exposed to DNA crosslinking drugs and environmental agents that promote lipid peroxidation (LPO), a likely source of endogenous ICLs, to determine if these exposures exacerbate the progeroid symptoms of the mice. The investigators discovered a human progeria caused by mutation of XPF. Thus identifying the cause of rapid aging in ERCC1-XPF-deficient mice will have direct implications for human health. The specific aims of this project are: Aim I: To define the cellular response of ERCCl-XPF-deficient cells to DNA ICLs and LPO. ERCCl-XPF-deficient cells will be exposed to 8-MOP or angelicin, plant-derived psoralens. Photoactivation of 8-MOP induces ICLs and monoadducts, whereas angelicin produces only monoadducts. Cell survival, cellular senescence, apoptosis, mutation frequency and chromosomal aberrations will be measured. If our hypothesis is correct then, 8-MOP will be significantly more cytotoxic than angelicin under conditions where an equal number of DNA lesions are induced. ERCCl-XPF-deficient cells will also be exposed to cadmium, an environmental agent that promotes LPO, to determine if LPO elicits the same cellular response as ICLs. Aim II: To directly test the hypothesis that unrepaired DNA ICLs promote aging. ERCC1-XPF hypomorphic mice will be chronically exposed to the crosslinking agent mechlorethamine. A second cohort will be exposed to 2-chloroethylamine (which induces structurally related monoadducts but not ICLs) using a dose that induces the same number of lesions as mechlorethamine. If our hypothesis is correct, mechlorethamine, but not 2-chloroethylamine, will exacerbate the progeria in these mice. Results will be confirmed by comparing skin aging in response to topical 8-MOP versus angelicin plus UV-A in mice genetically deleted for ERCC1-XPF in the skin only. Aim III: To determine if lipid peroxidation (LPO) promotes aging in mice with defective ICL repair. LPO is caused by oxygen radical damage to membranes and yields products able to crosslink DNA. We hypothesize that LPO is a source of ICLs that contribute to the phenotype of the Erccl mice. LPO will be induced in ERCCl-XPF-deficient mice via exposure to CCL4 or cadmium. If our hypothesis is correct, Erccl mice will be hypersensitive to LPO compared to wild type mice and LPO will exacerbate their progeria. Results from these experiments will indicate if LPO promotes aging and if so, whether it does so by inducing DNA damage. These experiments will also reveal if two common industrial exposures promote aging.