PPARγ介导母体吸烟致子代脂肪细胞发育编程改变及肥胖的表观遗传机制

Evidence shows that maternal smoking is closely related to an obese offspring in its adulthood, but the mechanism is not yet clear. The development and differentiation of adipose cell is of vital importance to developing obesity. Pregnancy and lactation is the key period in adipose cell differentiation and peroxisome proliferator-activated receptor gamma (PPARγ) is the key transcription factor regulating this differentiation process, the abnormal expression of which is closely related to obesity. It has been reported that the expression level of PPARγ is manipulated by epigenetic modification(DNA methylation or histone modification); in weaning offspring, prenatal nicotine exposure leads to higher PPAR γ expression level; there are several articles suggesting that nicotine in smoke plays the leading role in increasing offspring susceptibility to obesity, nicotine directly controls the expression and activity of DNMTs and HDACs through binding to receptors. Smoking or nicotine regulates the expression level of a variety of genes in different tissues(for example, PPARγ in fetal lung).Therefore, this project is designed to research the effect of nicotine with animal experiment, to explain how maternal smoking during pregnancy and lactation period affects adipose cell PPAR γ gene expression by epigenetic modification, adipose cell programming and obesity susceptibility in its offspring, and further reveal its epigenetic mechanism on cellular and molecular level. Hoping to verify and elaborate the link of "maternal smoking during pregnancy and lactation- - abnormal epigenetic modification to PPARγ gene in adipose cells in its offspring- - altered adipose cell programming of offspring at early development stage - - increased adult obesity susceptibility". This study is important in elucidating developmental origin of obese in its offspring caused by maternal smoking.

文献提示，母体吸烟与子代成年肥胖关系密切但机制不清。脂肪细胞的发育和分化在肥胖发生中至关重要，其中孕期/哺乳期是关键时期，转录因子PPARγ是核心调节因子。已证实，PPARγ易受表观遗传修饰（甲基化/乙酰化）调控；孕期母体吸烟，断奶时子代PPARγ增加；烟雾中尼古丁对后代肥胖易感起主要作用，尼古丁通过结合受体直接调控表观遗传相关酶表达与活性；吸烟或尼古丁可通过表观遗传修饰调节多种组织不同基因的表达（如胎肺PPARγ）。本项目拟以烟雾中的尼古丁为研究对象，利用动物实验证实孕期/哺乳期母体吸烟对子代脂肪细胞PPARγ表观遗传调控、脂肪细胞编程及肥胖的影响，并在细胞和分子水平阐明其表观遗传机制。以建立"孕期/哺乳期母体吸烟（尼古丁）-子代脂肪细胞PPARγ基因表观遗传修饰异常-发育早期脂肪细胞编程改变-成年肥胖易感性增加"之间的直接联系。该研究对解析母体吸烟致子代肥胖的发育起源具有重要意义。

肥胖现已成为全球性的公共卫生问题。流行病学调查表明，孕期及哺乳期母体尼古丁摄入可致子代肥胖及代谢综合征易感性增加，但其机制研究甚少。本项目旨在研究孕期及哺乳期母体尼古丁摄入引起子代肥胖的发育起源。建立孕期及哺乳期尼古丁暴露致子代大鼠成年后肥胖易感模型，利用HE染色及电镜观察脂肪组织及肝脏形态学改变; 检测子代血脂改变; 利用ELISA法检测血清胰岛素、瘦素及脂联素含量；利用实时定量PCR检测成脂分化、脂肪细胞因子、脂质代谢、糖代谢相关基因表达; 利用IPGTT和ITT实验检测子代大鼠胰岛素敏感性及葡萄糖耐受性。结果发现，尼古丁暴露引起母鼠体重减轻、脂肪量减少以及糖脂代谢紊乱，肝脏和脂肪脂合成及糖代谢相关基因表达明显降低。尼古丁暴露子代大鼠断奶时体重及脂肪量增加、脂肪组织成脂分化及脂合成相关基因表达增加，新生脂肪细胞数量增多，但肝脏脂质合成相关基因表达降低；出生后12、26周，尼古丁暴露组雄性子代脂肪量显著增加，出现血脂代谢紊乱、胰岛素抵抗以及糖代谢异常，脂肪组织成脂分化及脂合成相关基因表达增加，肝脏脂质合成转录因子及相关酶基因表达显著增加。此外，母体尼古丁暴露可致子代雄性大鼠棕色脂肪白色化、线粒体结构受损以及线粒体功能相关基因表达异常。细胞实验也发现，尼古丁可促进3T3L1前体脂肪细胞成脂分化。因此，孕期及哺乳期尼古丁暴露可致子代成年后肥胖易感、脂代谢紊乱及胰岛素抵抗。其主要机制与促进子代脂肪组织早期成脂分化及脂合成，并通过对脂肪组织的“编程”作用影响成年后体重、脂肪量及代谢有关。孕期及哺乳期尼古丁暴露引起的母体代谢改变可能也会对子代体重及代谢异常产生间接作用。此外，孕期及哺乳期尼古丁暴露可致子代大鼠棕色脂肪结构和功能异常是又一重要机制。本研究对于深刻阐明母体尼古丁暴露导致子代肥胖易感发生机制，解析肥胖的发育起源皆具有重要的理论价值和现实意义。