PP2Ac甲基化调控脂质自噬在苯并芘促进非酒精性脂肪性肝病中的作用研究

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic noncommunicable liver disease worldwide. It is reported that benzo[a]pyrene (BaP) promoted NAFLD but the mechanism is not clear yet. Recent researches showed that lipophagy is one of the key molecular events in the promotion of NAFLD, which can be regulated by the methylation of protein phosphatase 2A catalytic subunit (PP2Ac). It is not known yet that whether the PP2Ac methylation regulated lipophagy play a key role in the environmental chemicals promoting NAFLD. Our preliminary results showed that BaP can disturb PP2Ac methyaliton balance, which implies that BaP might interfere with hepatic lipophagy to promote NAFLD through PP2Ac methylation. To test the hypothesis, we will regulate PP2Ac methylation level in cells and animals by upregulating or downregulating the enzymes which specifically catalyzed PP2Ac methylation/demethylation; or by adjusting its active methyl group donor, to confirm the key role of PP2Ac methylation regulated lipophagy in BaP induced hepatic cell lipid accumulation and NAFLD. The protective effect of above regulating strategies against BaP promoting NAFLD will be explored as well. We will also explore the correlation between BaP internal exposure and biomarkers of PP2Ac methylation and autophagy, and NAFLD incidence in an established cohort using nested case-control study. This project will provide useful information on understanding the mechanism of environmental chemicals related NAFLD and give clues on prevention and treatment on NAFLD.

非酒精性脂肪性肝病（NAFLD）是第一大慢性非传染性肝病，苯并芘诱导脂质代谢紊乱促进NAFLD发生但机制未明。近期研究显示脂质自噬是NAFLD关键分子事件，可受蛋白磷酸酶2A催化亚基(PP2Ac)甲基化调控，但未知其在环境化学污染物促NAFLD中的作用。课题组前期研究发现苯并芘干扰肝细胞PP2Ac甲基化平衡，推测其通过调控PP2Ac甲基化而抑制脂质自噬，诱导肝脏脂质沉积，促进NAFLD。本研究拟采用正、反向调控PP2Ac甲基化特异催化酶及活性甲基供体的方式，在细胞及动物水平调节PP2Ac甲基化水平，以明确PP2Ac甲基化调控脂质自噬在苯并芘促NAFLD病理机制中的作用及上述调控方式的干预效果。并在已建立的队列人群采用巢式病例对照研究探讨苯并芘内暴露剂量与PP2Ac甲基化和自噬相关标志及NAFLD之间关系。本研究为深入理解环境化学污染物对NAFLD的影响及机制，并寻找干预措施提供科学依据。

非酒精性脂肪性肝病（NAFLD）是第一大慢性非传染性肝病，可进一步发展为非酒精性肝炎、肝硬化和肝癌，是当今重要的公共卫生问题。苯并芘是常见的环境化学污染物，低剂量苯并芘暴露可能诱导脂质代谢紊乱促进NAFLD发生。本研究在体外和体内探讨了低剂量苯并芘刺激对肝细胞脂肪沉积的促进作用及其机制，明确苯并芘对NAFLD促进作用的关键信号通路，同时探讨了该关键通路在肝癌发生中的作用。结果显示，低剂量苯并芘可在体外培养细胞和体内动物实验促进肝细胞脂肪沉积，LCMT1-PP2A通路在低剂量苯并芘促进NAFLD中发挥关键作用，并且LCMT1促进肝癌细胞增殖，是肝癌预后不良的生物标志。具体结果体现在：1.低剂量苯并芘促进肝细胞脂肪沉积及小鼠肝脏甘油三酯含量增加，促进NAFLD形成；2.苯并芘促进肝脏脂肪沉积过程中伴随PP2Ac甲基化上调，LCMT1表达上调，细胞自噬抑制，而肝细胞脂肪合成及转运关键基因表达未见显著改变；抑制PP2A及mTOR均可拮抗低剂量苯并芘诱导的脂质沉积，提示LCMT1-PP2A-mTOR通路诱导的自噬抑制是低剂量苯并芘促进NAFLD的重要机制；3.小鼠肝脏特异性敲除LCMT1可下调肝脏PP2A甲基化水平，同时缓解低剂量苯并芘诱导的小鼠肝脏脂肪沉积；4.LCMT1在肝癌组织高表达预示不良结局，LCMT1敲除通过抑制糖酵解和氧化磷酸化减少细胞内ATP生成从而抑制肿瘤细胞生长。上述结果显示，低剂量苯并芘可促进NAFLD形成，LCMT1-PP2A是NAFLD形成和肝癌细胞增殖的关键通路，LCMT1可作为肝癌预后不良的分子标志。本研究为深入理解低剂量苯并芘的生物效应以及肝脏脂肪性病变及肝癌形成和发展的机制提供科学证据，为NAFLD和肝癌的防治提供新的科学思路。