Fundamental molecular mechanisms of low dose radiation effects

了解低剂量电离辐射效应和体内适应性反应的基本分子机制一直是我实验室的重点研究支柱之一。2003-2004年，在我的nserc资助项目的范围内，我们率先在辐射表观遗传学领域进行了研究。我的NSERC计划的当前更新是基于我的小组对辐射反应中表观遗传变化作用的关键发现，并试图详细分析当生物体暴露于低剂量辐射时发生的基本表观遗传变化。我们将重点分析低剂量辐射（LDR），即剂量与因职业和环境照射而获得的剂量相当（0.1 Gy或更低）。最近的研究表明，低辐射辐射的生物效应非常复杂，生物体对辐射有很强的适应能力。辐射诱导的适应性反应机制仍然无法解释，可能是表观遗传的。表观遗传学的三个主要领域——DNA甲基化和羟甲基化、组蛋白修饰和小rna介导的沉默——已知对控制基因表达有深远的影响。虽然全球DNA甲基化在辐射反应中的作用已被证明，但这种表观遗传现象的确切性质需要被定义，其在LDR效应中的作用需要被确定。此外，辐射效应现象在DNA羟甲基化结构域尚未被探索。此外，需要更详细地分析小rna在LDR反应和辐射适应中的作用。NSERC项目更新的主要长期目标是解剖ldr诱导的基因组不稳定性和适应性反应的分子表观遗传基础，并确定表观遗传变化（即DNA甲基化、羟甲基化和小rna）在这些现象中的具体和基本作用。直接目标是：(i)调查LDR效应和适应性反应中全球和位点特异性DNA甲基化和DNA羟甲基化变化的确切性质；（ii）剖析调控小rna在LDR效应和适应性反应中的作用；（三）将表观遗传变化水平与细胞增殖、细胞死亡、DNA损伤和基因重排水平相关联，以及（四）分析适应性反应的年龄差异。我们将使用尖端的深度测序方法来表征甲基组、转录组和小RNAome，以测试我们的假设并实现我们的目标。本项目将为若干研究生、本科生和博士后提供良好的培养机会。除了揭示LDR反应的机制和分子表观遗传网络外，目前的项目还将解决一个根本性的重要问题：低剂量的环境辐射对生物体有危险吗？在福岛核事故之后，评估环境暴露的危害变得尤为重要。了解暴露的细胞和生物体中发生的分子变化可能有助于制定预防有害LDR效应的措施。使用小鼠模型获得的结果可以潜在地外推到其他生物体。因此，我的计划将提供对低剂量辐射反应的重要机理知识，并有助于减少低剂量风险评估的不确定性。

Understanding the fundamental molecular mechanisms of low-dose ionizing radiation effects and in vivo adaptive responses has been one of the key research pillars of my laboratory. In 2003-2004 within the scope of my NSERC-funded program, we pioneered the studies in the area of radiation epigenetics. The current renewal of my NSERC program is based on my group’s key discoveries of the roles of epigenetic changes in radiation responses, and seeks to analyze in detail fundamental epigenetic changes that occur when organisms are exposed to low doses of radiation. We will focus on analysis of low dose radiation (LDR), whereby doses are comparable to those acquired due to occupational and environmental exposures (0.1 Gy and lower). Recently it has been shown that the biological effects of LDR are very complex, and that living organisms have a great capacity to adapt to radiation. The mechanisms of radiation-induced adaptive responses remain unexplained, and may be epigenetic in nature. Three major areas of epigenetics - DNA methylation and hydroxymethylation, histone modifications and small RNA-mediated silencing - are known to have profound effects on controlling gene expression. While the role of global DNA methylation in radiation responses was shown, the exact nature of this epigenetic phenomenon needs to be defined, and its roles in LDR effects needs to be established. Furthermore, the phenomenon of radiation effects has not been explored in the DNA hydroxymethylation domain. Additionally, the roles of small RNAs in LDR responses and radioadaptation need to be analyzed in more detail. The main long-term goal of the renewal of this NSERC program is to dissect the molecular epigenetic basis of induction of LDR-induced genome instability and adaptive responses and identify the specific and fundamental role of epigenetic changes (i.e., DNA methylation, hydroxymethylation and small RNAs) in these phenomena. The immediate objectives are: (i) to investigate the exact nature of global and locus-specific DNA methylation and DNA hydroxymethylation changes in LDR effects and adaptive responses; (ii) to dissect the roles of regulatory small RNAs in LDR effects and adaptive responses; (iii) to correlate the levels of epigenetic changes with the levels of cell proliferation, cell death, DNA damage, and genetic rearrangements, and (iv) to analyze age differences in adaptive responses. We will use cutting-edge deep sequencing approaches to characterize methylome, transcriptome and small RNAome to test our hypotheses and achieve our goals. This project will provide excellent training opportunities for several graduate and undergraduate students and postdocs. Besides uncovering the mechanisms and revealing the molecular epigenetic networks involved in LDR responses, the current project will address a fundamentally important issue: are low doses doses of environmental radiation dangerous for living organisms? Evaluating the hazards of environmental exposure is especially important nowadays, after the Fukushima radiation accident. Understanding the molecular changes that occur in exposed cells and organisms may assist in the development of measures to prevent deleterious LDR effects. The results obtained using the mouse model can potentially be extrapolated to other organisms. Thus, my program will provide important mechanistic knowledge of the response to LDR and help reduce the uncertainty of assessing risk at low doses.