Overactivation Of Notch Signaling In Mouse Endometrial Epithelium Abolishes Embryo Implantation

Implantation is one of the critical steps during early mammalian pregnancy,this process refers to the interaction between activated blastocyst and the uterus in receptive state,resulting close connection between the embryonic trophoblast and the endometrium.Failure implantation leads to infertility.Previous study has shown the mice with conditional overexpression of Notch1 intracellular domain（N1ICD）in their uteri driven by progesterone receptor（Pgr）-Cre are completely infertile.These mice have no glands in their uterus,but their endometrial epithelial cells express the uterine glands marker FOXA2 and LIF,one of the most important secretions of the glands.To further investigate whether endometrial epithelial-specific overexpression of N1ICD affects implantation,we have created a endometrial epithelial specific N1ICD overexpressing mouse model driven by lactoferrin（LTF）-Cre.We have first confirmed the success of model creating and the overexpression of N1ICD by genotyping and Real-time PCR.Then,Ltf^+/+Rosa26^N1ICD/+female mice and Ltf^Cre/+Rosa26^N1ICD/+female mice were mated with wild male mice and we found that Ltf^Cre/+Rosa26^N1ICD/+female mice are completly infertile.Further investigation has observed regular implantation sites in the uterus of Ltf^+/+Rosa26^N1ICD/+mice but not in Ltf^Cre/+Rosa26^N1ICD/+mice.However,when we collected blastocysts from both groups of mouse uterus on D4,no difference in blastocysts number and morphology between the two genotypes of mice were observed.Further,Ltf^Cre/+Rosa26^N1ICD/+mice have lost their ability to response to the artificial decidualization stimulation,indicating the embryo implantation failure caused by the endometrial epithelial specific overexpression of N1ICD is due to the impaired uterine receiptivity.Then,we have studied estrogen and progesterone signaling pathways which are major regulators of uterine reciptivity.Compared to Ltf^+/+Rosa26^N1ICD/+mice,there was no difference in PGR expression,while the expression of progesterone target genes Areg and Ihh were decreased in Ltf^Cre/+N1ICD^F/+mice uterus.In the uterus of Ltf^Cre/+N1ICD^F/+mice,the expression of ERαwas significantly higher in Ltf^Cre/+N1ICD^F/+mice and the expression of Muc1 and Ltf regulated by estrogen were increased as well.We further found that the proliferation of luminal epithelial cells on D4was siginificantly increased in Ltf^Cre/+N1ICD^F/+mice due to the excessive activation of the estrogen signaling pathway in the uteruses,resulting in the inability of the uterine cavity to close,leads to inhibition of the receptivity.The expression of Lif,a key regulator of embryo implantation,in the uterus of Ltf^Cre/+N1ICD^F/+mice was significantly reduced,which may caused the failure of embryo implantation.In conclusion,our study have proved that endometrial epithelial-specific overexpression of N1ICD driven by Ltf-Cre inhibits embryo implantation via affecting the receptivity of the uterus.