抗氧化酶基因5羟甲基胞嘧啶修饰在微囊藻毒素肝氧化损伤效应中的作用及机制

Microcystins（MCs) is the most serious toxins of the algal species when blue-geen algae happens，which can cause hepatic oxidative damage. The Nrf2/ARE pathway is the key antioxidant pathway, which can directly activate the expression of antioxidant enzyme to resist the oxidative damage of MCs. Our previous study found that MCs exposure can prevent the Nrf2/ARE pathway from activing the transcription of antioxidant enzymes include GST, SOD, GPx, thereby inhibiting its antagonistic action on the hepatic oxidative damage induced by MCs. But the mechanism is unclear. Our further study found that MCs could activate the expression of TETs, which is the key enzyme of 5-hydroxymethylcytosine (5hmC) modification. And the 5hmC modification at the promoter of GST, GPx, SOD gene might block the transcription of these genes. We speculate that MCs may induce the 5hmC modification at GST, GPx and SOD gene. Thereby block the transcription of GST, GPx and SOD which were actived by the Nrf2/ARE pathway and promote hepatic oxidative damage of MCs. This project aims to clarify how the 5hmC modification is induced by MCs. And the mechanism of the gene expression regulation of GST, GPx and SOD by 5hmC modification. And the effects of 5hmC modification on hepatic injury induced by MC-LR. All of the work will provide a theoretical basis to reveal the molecular mechanisms on hepatic injury of MCs and to explore a biomarker of liver damage induced by MCs for the future. And provide a new way to explore the chemopreventive and chemotherapeutic against the liver injury and the promoting hepatic cancer effect induced by MCs, which has the practical significance to reduce health hazards of MCs.

微囊藻毒素（MCs）污染严重威胁公众健康。Nrf2/ARE通路激活并诱导下游抗氧化酶基因转录是拮抗MCs肝氧化损伤的关键环节。我们前期研究发现，MCs暴露下，Nrf2/ARE通路激活，但抗氧化酶GST、SOD、GPx等的表达却被抑制，原因尚不清楚。进一步研究发现，MCs可诱导催化5羟甲基胞嘧啶（5hmC）修饰的关键酶TETs表达增加。有研究提示：①GST、GPx、SOD基因启动子区的5hmC修饰可阻断基因转录；②MCs可通过PP2A/TDG途径抑制5hmC代谢。据此我们推测，MCs可能通过“TETs→5hmC生成↑”和“PP2A/TDG→5hmC代谢↓”两条途径增强启动子区5hmC修饰，从而阻断GST、GPx、SOD等抗氧化酶基因表达，促进MCs肝氧化损伤。本项目拟在前期基础上，通过细胞、动物模型，阐明MCs通过调控5hmC修饰影响氧化损伤修复的相关机制，为MCs肝氧化损伤防治提供依据。

本研究目的是揭示5羟甲基化修饰在微囊藻毒素-LR（MC-LR） 肝损伤效应中的作用。研究通过收集了MC-LR 暴露人群样本，确立了藻毒素暴露与肝损伤及肝癌关联。通过构建慢性染毒致人肝细胞株L02 细胞恶性转化模型，以及低剂量慢性染毒诱导肝细胞氧化损伤的SD大鼠体内模型，得到了慢性损伤的剂量反应关系，为后期研究MC-LR 损伤肝细胞的机制提供了良好的基础。研究发现，MC-LR可造成肝细胞脂肪滴增多、线粒体肿胀、氧化损伤（活性氧升高、抗氧化蛋白酶活性抑制），并可导致肝细胞发生恶性转化。进一步的机制研究初步证实了基因甲基化、5羟甲基化修饰通过调控多条信号通路（包括但不限于p53、Wnt/β-catenin）参与了MC-LR 致肝细胞恶性转化的过程。该研究为下一步深入研究藻毒素如何通过调节基因甲基化、5羟甲基化修饰使肝细胞发生恶性转化提供了线索。