Investigating the Formation and Remodeling of Uterine Spiral Arteries during Pregnancy

Project Summary Proper uterine vascularization is critical for a healthy pregnancy. Abnormalities in uterine vascular density are associated with infertility. Moreover, incomplete remodeling of the spiral arteries (SAs), vessels which transport maternal blood into the placenta for maternal-fetal nutrient exchange, is associated with the hypertensive disorder preeclampsia. Although uterine blood vessels, especially SAs, play an essential role in supporting pregnancy, little is known about how these vessels develop and remodel. The objectives of this proposal are therefore to 1) characterize the formation of SAs on a cellular and transcriptional level, and 2) define the molecular mechanisms underlying SA remodeling. While it is known that SAs are present in the uterus by mid- gestation, a mechanism for their formation has not been previously proposed. Our preliminary data indicate that SAs do not form via vasculogenesis or arterial sprouting, two common mechanisms by which new arteries develop. Thus, we hypothesize that SAs form via an alternative mechanism: angiogenesis from uterine veins. In Aim 1, we will rigorously test this hypothesis using light sheet imaging, lineage tracing, and single nucleus RNA sequencing. Additionally, we have detected high expression of the vascular remodeling protein Angiopoietin 2 (ANG-2) in the uterus during pregnancy. ANG-2 destabilizes blood vessels in a number of developmental and pathologic contexts by promoting the dissociation of smooth muscle cells from endothelial cells. In the uterus, the loss of smooth muscle cells from SAs appears to initiate SA remodeling. We hypothesize that ANG-2 is required for this process. In Aim 2, we will use pharmacologic and genetic methods to investigate how loss of ANG-2 signaling affects SA remodeling and pregnancy outcomes. Together, these studies will bring novel insights into the mechanisms by which blood vessels form and remodel in the uterus, which could have important implications for our understanding of infertility, preeclampsia, and other vascular complications of pregnancy.