滋养细胞PPARγ经外泌体介导调控胎儿脂肪生成的机制研究

Compromised adipogenesis is the main feature of FGR fetus compare to normal fetus, while peroxisome proliferator-activated receptor γ (PPARγ) is the key regulator of adipogenesis that promoting lipid metabolism. Our preliminary data demonstrated that PPARγ phosphorylation is significantly impaired in FGR placenta, while metabonomic profiling FGR and normal placenta showed abnormal accumulation of unsaturated fatty acid and decreased energy metabolism are associated with FGR placenta, in addition, differentiation and maturity of preadipocytes can be significantly improved after co-culture with trophoblast cells. Thus, we hypothesize that abnormal downregulation of PPARγ activity in FGR trophoblasts influence fatal preadipocytes through exosome, and then lead to impaired adipogenesis in offspring. Therefore, up-regulating PPARγ activity in trophoblast during pregnancy might be able to promote fetal adipogenesis, which is probably mediated by exosome, and ultimately improve fetal development and growth. This hypothesis will be validated from the perspective of tissue，cell and individual by the use of techniques of molecular biology, cell biology and pharmacology. The results of this study may elucidate the molecular mechanism underlying the crosstalk between placental trophoblasts and fetal adipocites at the feto-maternal interface, and investigate the possibility of regulating fetal adipogenesis by targeting trophoblast PPAR, which could further provide new therapeutic target and experimental evidence for FGR prevention and treatments.

脂肪生成障碍是FGR胎儿与正常胎儿的主要区别之一，而过氧化物酶体增殖物激活受体γ（PPARγ）是调节脂肪形成、促进脂类代谢最重要的因子。课题组前期研究发现FGR胎盘PPARγ磷酸化水平显著降低；胎盘代谢组学分析显示FGR胎盘存在不饱和脂肪酸异常蓄积及能量代谢降低；胎盘滋养细胞与前脂肪细胞共培养可明显促进后者的分化成熟及胞内脂滴聚集。由此推测FGR胎盘滋养细胞PPARγ活性异常下降可能通过外泌体介导调控胎儿前脂肪细胞分化，从而导致了胎儿脂肪生成障碍。因此在孕期上调滋养细胞PPARγ的活性将有可能通过外泌体介导的母胎对话促进胎儿脂肪生成，改善胎儿生长发育。本项目拟应用分子生物学、细胞生物学、药理学等方法从组织、细胞、个体三个层次验证上述假说，阐明滋养细胞与胎儿前脂肪细胞的母胎界面对话机制，探讨以滋养细胞PPARγ为靶点调控胎儿脂肪生成的可行性，为FGR防治提供新的思路和证据。

胎儿生长受限（fetal growth restriction, FGR）在我国的发生率为8.77%，是围生儿死亡的第二大原因。研究表明脂肪生成障碍是生长受限胎儿与正常胎儿的主要区别之一。过氧化物酶体增殖物激活受体γ（peroxisome proliferator-activated receptor γ, PPARγ）是调节脂糖代谢，促进脂肪分化成熟最重要的因子，但其在FGR发生发展过程中的作用机制至今未明。本课题围绕“滋养细胞PPARγ经外泌体介导调控胎儿脂肪生成的机制研究”展开研究。发现：（1）PPARγ在FGR胎盘组织中的表达水平及活性均明显降低，脂肪酸代谢通路中的各种因子如ACC及PGC-1α的活性在FGR胎盘组织中均有不同程度下降，而各孕周胎盘组织油红O染色并未发现胎盘组织本身存在脂肪生成差异。（2）HTR8/SVneo细胞与3T3-L1细胞共培养可明显促进3T3-L1及Tet PPARγ-KD 3T3-L1前脂肪细胞的分化成熟，而PPARγ敲降后的HTR8/SVneo细胞对3T3-L1细胞的分化成熟不再具有促进作用，与HTR8/SVneo - 3T3-L1细胞共培养相比，HTR8/SVneo细胞上清液外泌体与3T3-L1细胞共培养具有同样的促前脂肪细胞分化作用，而去外泌体的HTR8/SVneo上清液及PPARγ敲降后的HTR8/SVneo外泌体对3T3-L1的分化成熟不再具有促进作用。（3）动物实验表明，RUPP手术可导致明显的胎鼠生长发育迟缓、胎鼠脂肪组织百分比下降，而从孕中期开始使用PPARγ激动剂罗格列酮之后，胎鼠的生长发育及胎鼠脂肪组织百分比均显著改善，且胎鼠脂肪组织中的脂肪代谢相关调控分子的表达均有不同程度的变化。（4）小鼠活体成像、双光子显微镜及共聚焦显微镜结果均显示，孕鼠胎盘组织分泌的外泌体可通过脐带转运至胎鼠体内。（5）各孕周孕鼠胎盘、胎鼠及不同胎鼠器官PPARγ表达检测显示，PPARγ在整个孕期的胎盘组织中均处于高表达状态，其表达量远远高于胎鼠的不同器官组织。本课题深入探讨了PPARγ在FGR病理生理过程中的作用，为FGR的机制研究提供了新的理论证据，为其早期干预提供了潜在的分子靶点，完成了计划研究内容，达到了预期科研目标。但FGR的具体病理生理过程及其防治，仍有待进一步研究。