Spatiotemporal functions of leukemia inhibitory factor in embryo attachment and implantation chamber formation.

Embryo implantation is crucial for successful pregnancy, requiring appropriate uterine responses to implantation-competent blastocysts. Molecular communication at the maternal-fetal junction governs this process. Leukemia inhibitory factor (Lif) plays a pivotal role in implantation across species. Lif is abundantly expressed in the glandular epithelium during blastocyst-receptive phase and is induced in the stroma surrounding attached blastocysts. While diminished Lif expression leads to infertility, its influence on peri-implantation uteri remains unclear. Therefore, we investigated the role of Lif in uterine physiology using its uterine-specific knockout (uKO) and uterine epithelial-specific KO (eKO) in mice. Lif eKO and uKO mice displayed infertility owing to failed embryo attachment. Recombinant Lif supplementation rescued the reproductive phenotype of Lif eKO mice, but not Lif uKO mice; however, recombinant Lif injection rescued embryo attachment in Lif uKO mice. RNA-seq analysis indicated that Lif governs uterine epithelial genes, but not embryonic genes, to facilitate embryo attachment via activating nuclear Stat3. Concordantly, three-dimensional imaging of the uterine epithelium revealed that luminal closure and crypt formation are regulated by the uterine Lif-Stat3 axis as well as the presence of blastocysts. Collectively, our findings shed light on previously unknown mechanism on how Lif influences uterine functions molecularly and physiologically during early pregnancy.