孕期咖啡因暴露所致子代成年高胆固醇血症发生的宫内编程机制

Epidemiological investigations have showed that hypercholesterolemia has a developmental origin, but its underlying mechanism have not known.We have previously confirmed that prenatal caffeine exposure induces an increased susceptibility to metabolic syndrome in adult offspring rats, which was associated with intrauterineneuroendocrine metabolic programming alteration. Recently, we found that prenatal caffeine exposure induces hypercholesteremia in adult offspring, and the fetal hepatic sterol regulatory element binding protein 2 (SREBP2) and HMG CoA reductase (HMGCR) mRNA levels were enhanced. Based on literature, we hypothesize that prenatal caffeine exposure could inhibit the expression of fetal hepatic peroxisome proliferator activated receptorγ (PPARγ) by antagonism of adenosine receptor 2a(A2aR), which could up-regulate hepatic SREBP2 expression, and then enhance the histone acetylation and expression levels of cholesterol synthesisenzymes in the fetal liver. These alterations could continue to adulthood and induce hypercholesteremia. This project plan to explore the internal connection of “caffeine—inhibited A2aR/PPARγ expression levels—increased SREBP2 expression—enhanced histone acetylation levels and expression levels of cholesterol synthesisenzymes in fetal liver—adult hypercholesteremia”, and clarify the intrauterine programming mechanism of prenatal caffeine exposure induces hypercholesteremia in adult offspring rats. This study will provide a valuable experimental basis for explaining the fetal originated hypercholesteremia.

流行病学调查表明，高胆固醇血症存在宫内发育起源。本室前期发现，孕期咖啡因暴露的成年子代代谢综合征易感，并提出宫内神经内分泌代谢编程机制。我们近期发现，孕期咖啡因暴露的成年子代存在高胆固醇血症，且胎肝固醇调节元件结合蛋白2（SREBP2）和羟甲二酸单酰辅酶A还原酶（HMGCR）表达增加。综合文献，我们推测：咖啡因通过拮抗胎肝腺苷受体2a（A2aR）并抑制过氧化物酶体增殖物激活受体γ（PPARγ）表达，引起SREBP2表达升高，后者可增加胎肝胆固醇合成关键酶组蛋白乙酰化修饰及表达；此效应可持续至出生后，导致成年高胆固醇血症。本项目拟从整体和细胞水平，探讨“咖啡因—A2aR/PPARγ降低—SREBP2表达上调—胎肝胆固醇合成酶系统组蛋白乙酰化及表达增加—出生后高胆固醇血症”之间的联系，阐明孕期咖啡因暴露致子代高胆固醇血症的宫内编程机制，为探寻胎源性高胆固醇血症的早期防治，提供理论与实验依据。

临床和动物研究表明，高胆固醇血症具有宫内发育起源。我们以前的研究表明，孕期咖啡因暴露（PCE）可致成年子代血总胆固醇（TCH）水平升高。然而，其宫内发生编程机制至今尚不明确。本项目以日常生活中常见外源物——咖啡因为代表，发现PCE可引起子代大鼠宫内发育迟缓（IUGR），成年后大鼠高胆固醇血症易感。其发生机制与咖啡因激活肝脏胆固醇合成、咖啡因所致母源性糖皮质激素（GC）过暴露编程有关。宫内咖啡因抑制肝细胞腺苷受体（A2AR）/环磷酸腺苷（cAMP）/蛋白激酶A（PKA）通路进而下调去乙酰化酶SIRT1表达，导致胆固醇合成相关基因（SREBP2、HMGCR、HMGCS）的组蛋白乙酰化（H3K14ac和H3K27ac）水平及表达增加并延续至成年。同时，PCE导致母鼠血胆固醇水平升高，胎盘胆固醇转运功能抑制，胎盘GC屏障打开，引起胎儿“母源性GCs过暴露”，激活子代肝脏糖皮质激素受体（GR）/CCAAT增强子结合蛋白（CEBPα），进一步在Sirt1的协同下通过表观遗传修饰调控上调胆固醇合成基因羟基甲基二酸单酰辅酶A还原酶（HMGCR）乙酰化修饰水平（H3K9ac及H3K14ac）及表达，这种咖啡因和皮质酮调控下表遗传参与的胆固醇代谢编程效应可从宫内持续至成年，最终引起子代成年高胆固醇血症发生。最后，我们在PCE所致IUGR模型上进行了成年大鼠的高胆固醇血症易感与子代性别及出生后营养环境等因素的相关性分析，并发现疾病发生与子代出生后营养环境、性别之间存在交互作用。高脂饮食（HFD）可加重PCE所致子代高胆固醇血症，其发生机制与HFD加重肝脏胆固醇代谢紊乱有关。这种交互作用存在性别差异。雌性PCE组子代大鼠肝脏胆固醇酶改变较雄性PCE组明显。本项目首次阐明“成年高胆固醇血症具有胎儿起源”的宫内编程机制，为解析了国际前沿问题——“健康与疾病的发育起源”（DOHaD学说）提供了理论与实验依据。基于此项目我们获得了一些原创性研究成果，包括发表SCI论文3篇（1篇标注），会议摘要两篇（2篇标注），1篇墙报获评优秀。