MEHP对PPARγ靶基因核小体定位的影响及其在脂肪细胞分化中的作用

Mono (2-ethylhexyl) phthalate (MEHP) is the major metabolite of Di-(2-ethylhexyl) phthalate (DEHP) that is a widely used plasticizer. Exposure to MEHP can promote adipocyte differentiation and induce fat accumulation, which is may be associated with the change in the interaction of transcription factor peroxisome proliferator-activated receptor γ (PPARγ) and its target genes induced by MEHP, but the underlying molecular mechanism remains obscure. Based on the previous studies that nucleosome positioning within the promoter plays an important role in the regulation of transcription through interaction with transcription factors and transcription factors binding sites, the research will investigate the effect of MEHP on nucleosome positioning within the promoters of PPARγ target genes in different stages of adipocyte differentiation, and analyze the relationship between nucleosome positioning and the transcription levels of PPARγ target genes. Some representative PPARγ target genes with different levels of transcription will be selected to study the effect of MEHP on the interaction of PPARγ and the response elements on the specific target genes, and its association between nucleosome positioning will be assessed. The status of the main regulators of nucleosome positioning, including chromatin remodeling complex and histone modification, will be studied. In addition, the study will verify the above results in mice perinatally exposed to MEHP. The research will illustrate the role of nucleosome positioning within the promoters of PPARγ target genes in adipocyte differentiation, and provide new insights for the mechanism of adipocyte differentiation induced by MEHP and other similar environmental chemicals.

邻苯二甲酸单乙基己基酯（MEHP）是增塑剂邻苯二甲酸二乙基己基酯的主要代谢产物，MEHP暴露可促进脂肪细胞分化，增加脂质积累，研究发现这可能与MEHP引起的转录因子PPARγ与其靶基因相互作用的改变有关，但机制仍待阐明。本研究从核小体定位可影响转录因子与靶基因结合从而对转录调控起重要作用的新思路出发，拟采用前脂肪细胞系(3T3-L1)，分析MEHP对分化不同时期PPARγ的靶基因启动子区核小体定位模式的影响及其与靶基因转录水平之间的关联，研究MEHP导致的核小体定位改变对PPARγ和靶基因反应元件结合的影响，并测定MEHP暴露后靶基因启动子区核小体定位的主要调节因素，并在发育期暴露MEHP的小鼠模型中进行验证，阐明MEHP对PPARγ的靶基因核小体定位的影响及其在脂肪细胞分化中的作用。本项目的开展有助于揭示MEHP促脂肪细胞分化的机制，并为类似化学物质引起肥胖的机制研究提供新的线索。

近年来全球肥胖率显著上升，除了遗传、不良饮食和缺乏运动以外，越来越多的证据表明，某些环境污染物的暴露与肥胖的发生也密切相关。邻苯二甲酸单-2-乙基己基酯（MEHP）是增塑剂邻苯二甲酸二乙基己基酯（DEHP）的主要代谢产物。MEHP在环境中广泛存在，进入人体后易存储在脂肪组织中。目前有动物实验及少量人群研究提示MEHP可能是一种致肥胖因子，但具体机制不明。本项研究发现环境水平的MEHP可促进前脂肪细胞的分化及脂质聚集，并揭示了PPAR γ与靶基因相互作用的改变是其影响脂肪细胞分化及脂质聚集的关键机制之一，PPAR γ的靶基因启动子区的核小体定位状态可影响PPAR γ与靶基因的结合，从而调控靶基因的转录，其中染色质重塑复合物（SWI/SNF）参与调控基因的转录；并在发育期MEHP暴露的小鼠动物模型上验证了上述结果。此外，该研究明确了处于脂肪细胞发育分化关键期胎儿的邻苯二甲酸酯的内暴露水平，并发现了DEHP代谢产物暴露水平的增加与新生儿体重和旁氏指数的增加相关，提供了DEHP代谢产物暴露可增加肥胖风险的人群证据，从而验证了毒理实验发现的MEHP促进脂肪细胞分化和脂质聚集的结果。本项目揭示了MEHP促前脂肪细胞分化和脂质聚集的机制，研究成果在Environment International（IF=7.08）、Science of The Total Environment （IF=4.90）、Journal of Applied Toxicology等国际专业杂志上共发表SCI论文12篇，为类似化合物引起肥胖的机制研究及疾病预防靶点提供了新的线索。