Differential expression of VEGF isoforms and VEGF164-specific receptor neuropilin-1 in the mouse uterus suggests a role for VEGF164 in vascular permeability and angiogenesis during implantation

Summary: The mechanism(s) by which localized vascular permeability and angiogenesis occur at the sites of implantation is not clearly understood. Vascular endothelial growth factor (VEGF) is a key regulator of vasculogenesis during embryogenesis and angiogenesis in adult tissues. VEGF is also a vascular permeability factor. VEGF acts via two tyrosine kinase family receptors: VEGFR1 (Flt-1) and VEGFR2 (KDR/Flk-1). Recent evidence suggests that neuropilin-1 (NRP1), a receptor involved in neuronal cell guidance, is expressed in endothelial cells, binds to VEGF165 and enhances the binding of VEGF165 to VEGFR2. We examined the spatiotemporal expression of vegf isoforms, nrp1 and vegfr2 as well as their interactions in the periimplantation mouse uterus. We observed that vegf164 is the predominant isoform in the mouse uterus. vegf164 mRNA accumulation primarily occurred in epithelial cells on days 1 and 2 of pregnancy. On days 3 and 4, the subepithelial stroma in addition to epithelial cells exhibited accumulation of this mRNA. After the initial attachment reaction on day 5, luminal epithelial and stromal cells immediately surrounding the blastocyst exhibited distinct accumulation of vegf164 mRNA. On days 6–8, the accumulation of this mRNA occurred in both mesometrial and antimesometrial decidual cells. These results suggest that VEGF164 is available in mediating vascular changes and angiogenesis in the uterus during implantation and decidualization. This is consistent with coordinate expression of vegfr2, and nrp1, a VEGF164-specific receptor, in uterine endothelial cells. Their expression was low during the first 2 days of pregnancy followed by increases thereafter. With the initiation and progression of implantation (days 5–8), these genes were distinctly expressed in endothelial cells of the decidualizing stroma. Expression was more intense on days 6–8 at the mesometrial pole, the presumptive site of heightened angiogenesis and placentation. However, the expression was absent in the avascular primary decidual zone immediately surrounding the implanting embryo. Crosslinking experiments showed that 125I-VEGF165 binds to both NRP1 and VEGFR2 present in decidual endothelial cells. These results suggest that VEGF164, NRP1 and VEGFR2 play a role in VEGF-induced vascular permeability and angiogenesis in the uterus required for implantation. genesis 26:213–224, 2000. © 2000 Wiley-Liss, Inc.