MEKK4磷酸化修饰HoxA10促进子宫内膜容受性与胚胎种植的机制研究

HoxA10 has been shown to be important for endometrial receptivity, but little is known about the mechanism of HoxA10 being regulated during embryo implantation. Previous studies showed that HoxA10 expression is decreased in the endometrium of patients with receptivity defects. Interestingly, we found that the protein levels of HoxA10 were not reduced in the endometrium of RIF (repeated implantation failure) women, but HoxA10 phosphorylation was apparantly inhibited in the endometrium of RIF patients. The result of mass spectrometry also showed that HoxA10 was indeed phosphorylated in mouse endometrium during peri-implantation period. Our findings indicate that phosphorylation of HoxA10 may play vital roles for embryo implantation. Further study revealed that MAP kinase kinase kinase 4 (MEKK4), specifically expressed in human endometrial epithelial cells (hEEC), interacted with HoxA10 in hEEC. The levels of MEKK4 and phosphorylated HoxA10 were dramatically induced in hEEC treated with estrogen plus progesterone and in mouse endometrium during peri-implantation period. Therefore, our hypothesis is that MEKK4 promotes the development of endometrial receptivity and embryo implantation through promoting HoxA10 phosphorylation. The main focus of this study is on confirming the role of MEKK4 in regulating endometrial receptivity and embryo implantation by enhancing HoxA10 phosphorylation. Our study may provide us a novel insight for the mechanism of implantation failure in IVF-ET.

子宫内膜容受性关键调控分子HoxA10转录活性的调控机制目前不清。以往研究报道提示HoxA10的表达减少与子宫内膜容受性缺陷相关，但我们发现HoxA10蛋白在部分反复种植失败患者内膜中表达并未减少，其磷酸化水平明显降低，同时蛋白质谱鉴定结果表明围种植期小鼠子宫组织中HoxA10蛋白存在磷酸化修饰，提示HoxA10蛋白磷酸化修饰在胚胎种植过程中可能具有重要调节作用。我们前期研究证实MEKK4主要表达于人子宫内膜上皮细胞中，并与HoxA10相互结合；MEKK4蛋白的表达和HoxA10蛋白磷酸化修饰在雌孕激素联合刺激人子宫内膜上皮细胞中和围种植期小鼠子宫中明显增加。因此，我们推测MEKK4可能通过促进HoxA10磷酸化修饰调节子宫内膜容受性和胚胎黏附。本项目将重点探讨MEKK4磷酸化修饰HoxA10对子宫内膜容受性与胚胎种植的调控作用，以期阐明临床不孕患者IVF-ET周期中种植失败的分子机制。

子宫内膜容受性关键调控分子HoxA10转录活性的调控机制目前不清。以往研究报道提示HoxA10的表达减少与子宫内膜容受性缺陷相关，但我们发现HoxA10蛋白在部分反复种植失败患者内膜中表达并未减少，其磷酸化水平明显降低，同时蛋白质谱鉴定结果表明围种植期小鼠子宫组织中HoxA10蛋白存在磷酸化修饰，提示HoxA10蛋白磷酸化修饰在胚胎种植过程中可能具有重要调节作用。我们通过调查发现丝氨酸/苏氨酸蛋白激酶MEKK4特异性表达于人子宫内膜上皮细胞且在分泌期表达显著升高，而在反复种植失败患者子宫内膜上皮细胞中MEKK4表达显著降低，过表达MEKK4可促进子宫内膜容受性标志分子integrin β3表达。因此，我们推测MEKK4可能通过促进HoxA10磷酸化修饰调节子宫内膜容受性和胚胎黏附，体外实验证实MEKK4与HoxA10相互结合并促进HoxA10磷酸化修饰及其转录活性。此外，我们还发现孤儿核受体Nur77可直接与HoxA10启动子相结合，靶向调控HoxA10蛋白表达，进而影响胚胎黏附。我们针对子宫内膜容受性关键分子HoxA10蛋白翻译后修饰及转录水平调控的研究为揭示种植失败机制和提高不孕症患者临床妊娠成功率提供新的研究方向和靶点。