Effects of tibolone and its metabolites on Angiopoietin-1, Tie-2 and tumor necrosis factor-alpha mRNA in Ishikawa cells. Implication for tibolone's effects on the endometrium

Divergent regulation of angiopoietin-1 and -2, Tie-2, and thrombospondin-1 expression by estrogen in the baboon endometrium

Estrogen has an important role in the reconstruction of a new vascular network in the endometrium during each menstrual cycle; however, the underlying mechanisms are incompletely understood. Angiopoietin-1 (Ang-1) promotes vessel assembly, whereas Ang-2 and thrombospondin-1 (TSP-1) cause vessel breakdown. To determine the potential effect of estrogen on the expression of these angioregulatory factors in the endometrium, Ang-1, Ang-2, TSP-1, and Tie-2 receptor mRNA levels were assessed by real-time reverse transcriptase polymerase chain reaction in glandular epithelial and stromal cells isolated from the endometrium of ovariectomized baboons treated acutely with estradiol. Corresponding protein expression was assessed by immunocytochemistry and the proximity ligation assay (PLA) during advancing stages of the baboon menstrual cycle. Serum estradiol levels in ovariectomized baboons were 400 pg/ml within 4-6 hr of estradiol treatment. Ang-1 mRNA levels in glandular epithelial cells increased threefold (P < 0.01) within 4 hr of estradiol administration. In contrast, TSP-1 mRNA levels decreased four- to fivefold (P < 0.01) in endometrial glandular epithelial and stromal cells 4-6 hr after estradiol, whereas Ang-2 and Tie-2 expression was unaltered. Immunostaining for Ang-1 increased, TSP-1 decreased, and Ang-2 and Tie-2 were unaltered in the endometrium during the secretory compared with the proliferative phase of the cycle. Endometrial Ang-1 protein expression, quantified by PLA, increased 10-fold (P < 0.05) between the early proliferative and late proliferative/mid-secretory phases of the menstrual cycle in association with the rise in estrogen. In summary, estrogen induced a rapid, divergent, and cell-specific change in expression of angiostimulatory and angioinhibitory growth factors in the endometrium of the nonhuman primate.

Estrogen stimulates the human endometrium to express a factor(s) that promotes vascular smooth muscle cell migration as an early step in microvessel remodeling

Vascular smooth muscle cell (VSMC) migration is a pivotal early step in blood vessel remodeling; however, very little is known about the regulation of this process in the human endometrium during the menstrual cycle. In this study, explants of human endometrium were incubated with estradiol and/or progesterone and the conditioned medium (CM) applied to cultures of VSMC to test the hypothesis that estrogen and progesterone stimulate endometrial cells to secrete a factor(s) that promotes VSMC migration. Endometrial explants were composed of highly organized glands and stroma. VSMC migration (cells migrated in 21 h/mm(2) fibronectin-coated semipermeable membrane) in the presence of CM from human endometrial explants obtained in the proliferative phase of the menstrual cycle and incubated for 24 h with estradiol was approximately threefold greater (P < 0.001) than with medium alone and greater (P < 0.05) than with CM from explants treated with estradiol plus progesterone or progesterone. It is concluded, therefore, that estrogen stimulates endometrial secretion of a factor(s) that promotes VSMC migration as an early step in vessel remodeling within the endometrium.