No abstract

The cyclic growth, differentiation, and cell death of endometrium represents the most dynamic example of steroid-driven tissue turnover in human adults. Key effectors in these processes-matrix metalloproteinases (MMPs) and their specific inhibitors (TIMPs)-are regulated by ovarian steroids and, locally, by cytokines. We used reverse transcription-polymerase chain reaction to evaluate the expression of both transcriptionally regulated molecules such as estrogen receptor-alpha, progesterone receptor, and prolactin and a large array of MMPs and TIMPs (MMP-1, -2, -3, -7, -8, -9, -11, -12, -19, -26, MT1-MMP, MT2-MMP, MT3-MMP, TIMP-1, -2, -3). Altogether, three distinct patterns of MMP and two patterns of TIMP expression were detected in cycling endometrium: 1). MMPs restricted to the menstrual period (MMPs-1, -3, -8, -9, -12); 2). MMPs and TIMPs expressed throughout the cycle (MMP-2, MT1-MMP, MT2-MMP, MMP-19, TIMP-1, and TIMP-2); 3). MMPs predominantly expressed during the proliferative phase (MMP-7, MMP-11, MMP-26, and MT3-MMP); and 4). TIMP-3, which, contrary to the other TIMPs, shows significant modulations, with maximum expression during the late secretory and menstrual phases. These specific patterns of MMP expression associated with each phase of the cycle may point to specific roles in the processes of menstruation, housekeeping activities, angiogenesis, tissue growth, and extracellular matrix remodeling.

Successful embryo development requires an extensive endometrial angiogenesis in proximity of implantation site. The glycoprotein hCG is produced even before implantation by trophoblast in normal pregnancy. In this manuscript, we demonstrate an angiogenic effect of hCG in several in vivo (chick chorioallantoïc membrane, matrigel plug assay, aortic ring assay) and in vitro experimental models. In contrast, human placental lactogen (hPL) did not display angiogenic properties. LH/hCG receptor was detected in endothelial cells by reverse-transcriptase polymerase chain reaction (RT-PCR) and by Western blotting. In mice aortic ring assay, angiostimulation by hCG was abrogated by deletion of LH/hCG receptor (LuRKO mice). Use of recombinant hCG and anti-hCG antibody (Ab) further confirmed the specificity of this angiogenic activity. By using dibutyryl cAMP, adenylate cyclase, or protein kinase A inhibitors, we demonstrate that hCG-mediated angiogenesis involves adenylyl-cyclase-protein kinase A activation. Addition of hCG to endometrial epithelial epithelial cells, but not to cultured endothelial cells, stimulated vascular endothelial growth factor (VEGF). VEGF and hCG also displayed additive activities. Altogether, these data demonstrate that peritrophoblastic angiostimulation may result from a paracrine dialogue between trophoblast, epithelial, and endothelial cells through hCG and VEGF.

Acceptance of the fetal semi-allograft by the mother’s immune system has become the focus of intensive research. CD4+ T cells are important actors in the establishment of pregnancy. Th1/Th2 paradigm has been expanded to include CD4+ regulatory T (Treg) and T helper 17 (Th17) cells. Pregnancy hormones exert very significant modulatory properties on the maternal immune system. In this review, we describe mechanisms by which the endocrine milieu modulates CD4 T cell polarization during pregnancy. We first focused on Treg and Th17 cells and on their importance for pregnancy. Secondly, we review the effects of pregnancy hormones [progesterone (P4) and estradiol (E2)] on immune cells previously described, with a particular attention to human chorionic gonadotropin (hCG). The importance of Treg cells for pregnancy is evidenced. They are recruited before implantation and are essential for pregnancy maintenance. Decreased number or less efficient Treg cells are implicated in fertility disorders. As for Th17 cells, the few available studies suggest that they have a negative impact on fertility. Th17 frequency is increased in infertile patients. With the combination of its pro-effects on Th2 and Treg cells and anti-effects on Th1 and Th17 cells, P4 contributes to establishment of a favorable environment for pregnancy. E2 effects are more dependent on the context but it seems that E2 promotes Treg and Th2 cells while it inhibits Th1 cells. hCG positively influences activities of Treg and uterine natural killer cells. This embryo signal is an essential actor for the success of pregnancy, both as the endocrine factor regulating P4 secretion by the ovarian corpus luteum, but also as a paracrine agent during implantation as well as an angiogenic and immunologic mediator during the course of gestation. Luteinizing hormone (LH) immune properties begin to be studied but its positive impact on Treg cells suggests that LH could be a considerable immunomodulator in the mouse.

Through hCG, the blastocyst may be involved in the control of its implantation (via an increase of proimplantatory LIF) and tolerance (via an inhibition of proinflammatory IL-6). Other growth factors present at the embryonic-endometrial interface are also involved in the control of LIF and IL-6 endometrial secretion.

VEGF111 accelerates blood vessel recruitment and functional angiogenesis and improves the viability of ovarian cortex by limiting ischemia and ovarian cortex damage.

Embryo implantation requires extensive angiogenesis at the maternal-fetal interface. Hyperglycosylated human chorionic gonadotropin (hCG-H), a trophoblast invasive signal produced by extravillous cytotrophoblasts and by choriocarcinoma, was evaluated for its angiogenic role. hCG-H was purified by HPLC from choriocarcinoma supernatant, and the glycosylation pattern was determined by 2D gel analysis. Angiogenesis models used were aortic ring assay with wild-type and LHCGR-knockout mice, endothelial and mural cell proliferation, and migration assays. The TGF-β signaling pathway was studied by coimmunoprecipitation, competitive binding, TGF-β reporter gene assays, and Smad immunoblotting. hCG-H displayed a potent angiogenic effect [3.2-fold increase of number of vessel intersections in wild-type aortic rings (11.406 to 36.964)]. hCG-H-induced angiostimulation was independent of the classic hCG signaling pathway since it persisted in LHCGR-knockout mice [4.73-fold increase of number of vessel intersections (10.826 to 51.288)]. Using TGF-β signaling inhibitors, Tβ-RII was identified as the hCG-H receptor responsible for its angiogenic switch. hCG-H exposure enhanced phosphorylation of Smad 2 in endothelial and mural cells and genomic activation of Smad-responsive elements. Interaction between hCG-H and Tβ-RII was demonstrated by coimmunoprecipitation and binding competition with (125)I-TGF-β. This new paracrine interaction between trophoblast and endothelial cells through the hCG-H and the TGF-β receptor complex plays a key role in angiogenesis associated with placental development and tumorigenesis.

Our findings highlight a novel paracrine role of this early embryonic signal in vessel maturation by stimulating perivascular cell recruitment, migration, and proliferation.