210. Localisation of insulin-like growth factor-II (IGF-II) and its receptor in early murine pregnancy: a role in placentation and angiogenesis in the decidua?

Abstract

The highly invasive activity of the human placenta is tightly regulated by a variety of growth factors and other molecules. Contrary to the dominant view, recent data suggests that IGF-II, upon binding to the IGF2R, can stimulate an intracellular signalling pathway.1 Evidence in humans and mice suggests that IGF-II and the IGF2R are important regulators of placental growth; however, to date they have not yet been localised to early murine implantation sites. This study provides a photo micrographic account of early placental development and the decidual vasculature in the mouse, and localises IGF-II and the IGF2R from days 5.5 to 10.5 of pregnancy. During early pregnancy, the decidua displays a paucity of blood vessels, which appear to undergo angiogenesis, so that by day 10.5 the decidua has become a highly vascularized structure, with an extensive network of dilated vessels that presumably enable maximal blood supply to the placenta. Unlike humans, murine trophoblast cells do not invade the endometrium individually, but remain in close contact with the main giant cell layer. The trophoblast giant cells (TGCs) are the outermost cell type of the murine placenta and maternal blood spaces beneath this layer are not lined by endothelium. Due to their location, TGCs appear to play a direct role in displacing this endothelium and therefore may play a role in the transformation into trophoblast lined maternal blood spaces. IGF-II and its receptor were present throughout early pregnancy in the conceptus and maternal decidua supporting their role as regulators of fetal and placental development. Most interesting, however, was their association with the developing maternal blood vessels in the mesometrial decidua. It seems likely that in mice the maternal vessels are remodelled by a variety of locally derived molecules. By association, IGF-II and its receptor are likely candidates. (1)McKinnon T, et al. (2001). Stimulation of human extravillous trophoblast migration by IGF-II is mediated by IGF type 2 receptor involving inhibitory G protein(s) and phosphorylation of MAPK. J. Clin. Endocrinol. Metab. 86(8), 3665–3674.