GC-SIRT1-SREBP1c信号介导孕期尼古丁暴露所致子代NAFLD易感的宫内编程机制

Epidemiological investigations have showed that non-alcoholic fatty liver disease (NAFLD) has developmental origin. In our previous studies, we have discovered that prenatal nicotine exposure may enhance susceptibility to intrauterine growth retardation (IUGR) and adult metabolic syndrome, and the mechanism is relative to overexposure to maternal glucocorticoids (GC). Furthermore, we have found that the expressions of hepatic SREBP1c increased in both the fetus and IUGR offspring. Based on literature, we hypothesize that high maternal GC induced by prenatal nicotine exposure may increase acetylation and expression of SREBP1c by reducing the expression of SIRT1 in the fetal liver, and enhance lipid synthesis in the liver. The effect can continue to after birth and mediate susceptibility to NAFLD. In the present study, we will intend to confirm that the phenomenon of susceptibility to NAFLD in IUGR offspring induced by prenatal nicotine exposure, clarify the molecular genetic mechanisms of intrauterine fetal programming of NAFLD, and determine the key position and possible regulatory mechanisms of GC-SIRT1-SREBP1c signaling pathway in fetal liver in the development and progression of NAFLD. We will furtherly intervene the expression of SIRT1 in the lab animals and cell levels to explore early intervention and prevention of measures of NAFLD caused by fetal original factors and to provide experimental basis.

流行性病学调查提示，非酒精性脂肪肝（NAFLD）存在宫内发育起源。我们前期发现，孕期尼古丁暴露可引起仔鼠宫内发育迟缓（IUGR）及成年后代谢综合征易感，其机制与母源性糖皮质激素（GC）过暴露有关；同时发现IUGR仔鼠出生前、后肝脏SREBP1c表达升高。综合文献，我们推测：孕期尼古丁暴露所致的母源性高GC，可通过降低胎肝SIRT1表达，增加SREBP1c乙酰化修饰及表达，使肝脏脂质合成功能增强，此效应可持续至出生后，从而介导NAFLD的易感性。本项目拟在整体与细胞水平，证实孕期尼古丁暴露所致IUGR子代的NAFLD易感现象，确定胎肝GC-SIRT1-SREBP1c信号在出生后NAFLD发生、发展过程中的关键地位及其转录调控机制，并在整体动物水平对SIRT1活性进行干预。本项目将为解析胎源性NAFLD宫内编程的分子遗传机制，探寻胎源性NAFLD的药物干预靶标及早期防治策略，提供实验依据。

孕期外源物暴露可致子代宫内发育迟缓（IUGR）和成年后代谢性疾病易感，其机制研究日渐深入。本室前期研究证实孕期外源物暴露致IUGR子代HPA轴低基础活性和高应激敏感性以及GC依赖性糖脂代谢编程改变。随着“健康与疾病的发育起源”（DOHaD）理论逐渐被学者关注，越来越多的研究发现孕期不良宫内环境可致子代非酒精性脂肪肝病（NAFLD）易感。本项目从NAFLD的胎源性发病机制着手，在整体水平证实孕期尼古丁暴露（PNE）所致IUGR子代的NAFLD易感现象，进一步在整体与细胞水平明确肝GC-SIRT1-SREBP1c信号在NAFLD发生、发展过程中的关键地位及其转录调控机制。本课题整体水平研究结果表明，PNE致子代肝脏甘油三酯合成功能增强，成年后NAFLD易感，其发生机制可能与宫内高GC通过增加肝脏GR表达，调控C/EBPα和Sirt1表达，从而介导肝脏SREBP1、FASN表达增强的宫内编程密切相关，且延续至出生后，致成年子代NAFLD易感。进一步，我们通过检测不同浓度的皮质醇对人胎肝细胞GR-C/EBP-Sirt1信号及TG代谢相关基因表达的影响，证实肝细胞甘油三酯蓄积，GR、C/EBP表达增加，Sirt1表达减少，甘油三酯合成增加，且呈一定的浓度依赖性；采用GR、C/EBPα干扰或Sirt1激动剂白藜芦醇干预皮质醇处理过的LO2细胞，检测高浓度皮质醇处理后的人胎肝细胞GR-C/EBPα-Sirt1信号通路各基因表达、SREBP1c及FASN乙酰化状态及表达、脂质合成酶表达的变化。结果表明GR/C/EBPα干扰可逆转皮质醇对GR-C/EBPα-Sirt1信号通路的影响和对SREBP1、FASN及其组蛋白乙酰化的促表达作用。白藜芦醇可逆转皮质醇的SREBP1、FASN mRNA促表达及组蛋白乙酰化增加效应，确定Sirt1参与GC调控SREBP1c及脂质合成功能的表观遗传调控机制，从细胞水平进一步验证了动物实验的结果，且首次从表观遗传学角度证实 SREBP1c/FASN 启动子区域H3K14ac和H3K27ac增加可能是该编程的基础。本项目还通过孕期多种外源物暴露建立IUGR模型，全面观察了IUGR个体的HPA轴功能及糖脂代谢改变，首次证实和系统解析了IUGR个体成年后NAFLD易感的宫内编程分子机制，为今后探寻胎源性NAFLD的早期防治策略和药物干预靶标，提供实验依据。