Regulation of protein synthesis and decidualization in the uterus
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In the uterine epithelium, steroid sex hormone estradiol-17beta (E2) induces coupled activation of DNA and protein synthesis. However, E2 and progesterone (P4) work together to induce a divergence between DNA and protein synthesis, where DNA synthesis is inhibited while protein synthesis persists. We aimed to determine the bifurcating mechanism of the two processes.;First we performed western blots and immunohistochemistry with mouse uterine samples. The results indicated that mTORC1 pathway is activated upon E2 and P4E2 stimulation in the uterine epithelium. Intraluminal injection of rapamycin inhibited mTORC1 activation, protein synthesis, DNA synthesis and artificially-induced decidualization, suggesting the important role of mTORC1 pathway in these events. Next we obtained human biopsies and their xenografts in mice and demonstrated a similar mTORC1 pathway activation. Similarly, rapamycin inhibited activation of the mTORC1 pathway and KI-67 labeling index in human xenografts. Therefore mouse and human may share the same mTORC1 regulation of protein synthesis in the uterine epithelium. Screening of upstream regulators with mouse samples identified that phosphorylation of PKC and ERK1/2 was stimulated by E2. In vivo studies with chemical modulators indicated that activation of the mTORC1 by E2 is mediated by a PKC-ERK1/2 pathway. Moreover, we demonstrated that activation of PKC-ERK1/2-mTORC1 is ER-dependent.;Furthermore, to test the biological relevance of STAT3 in the female reproductive system, we generated a mouse strain carrying uterine epithelial-specific ablation of Stat3 (Stat3UtEp/UtEp mice). Stat3UtEp/UtEp mice did not show defects in development and grew to adulthood. However, females of these mice displayed infertility. Further characterization indicated that Stat3 is required for decidualization and HAND2 expression in the uterine stroma during implantation.;In conclusion, the studies in this dissertation identified the mechanism of protein synthesis regulation in the uterine epithelium. Disruption of this mechanism resulted in severe abnormalities in the preparation of the uterus for implantation. Also, our genetic model demonstrated that STAT3 expression in the uterine epithelium is critical for the preparation of the uterus for implantation.