Oral Virtual Presentation (Virtual only) ESA-SRB-ANZBMS 2021

Alterations in placental endothelial and perivascular heterogeneity could contribute to the pathophysiology of fetal growth restriction (#152)

Anna L Boss 1 , Larry W Chamley 1 , Anna A.E.S Brooks 2 , Jo L James 1
  1. Obstetrics and Gynaecology, University of Auckland, Auckland, New Zealand
  2. Maurice Wilkins Centre & School of Biological Sciences, University of Auckland , Auckland, New Zealand

Placentae from FGR pregnancies are smaller, with a reduced vascular network that impairs placental exchange. However, little is known about the complex differentiation events and distinct cell types that underpin normal and abnormal placental vascular formation/function. We aimed to characterise the vascular and perivascular cell populations within the placental villous core across gestation, and determine whether differences exist in FGR placentae.

First-trimester (7-12 weeks, n=6), normal term (37-40 weeks, n=3), or FGR (<5th percentile, 37-40 weeks, n=3) placentae were denuded of trophoblast and enzymatically digested. The resulting cells were phenotyped using 23-colour flow cytometry. First-trimester (<9 weeks) endothelial cells (CD31+CD34+) were FACS sorted (n=3) and cultured in endothelial differentiation (EGM-2+VEGF165 on Matrigel) or smooth muscle differentiation (advanced-DMEM/F12+TGF-β1) conditions. Differentiation was assessed by multi-colour flow cytometry and immunohistochemistry.

Endothelial and perivascular cell phenotypes and heterogeneity differed across gestation. Proportionally, in FGR placentae endothelial cells constituted 3-fold fewer total villous core cells (p<0.05), contributing to an increased perivascular:endothelial cell ratio (2.6-fold higher, p<0.05). Term endothelial cells expressed “mature” endothelial markers (CD36+CD146+), whilst first-trimester demonstrated an “immature” phenotype (CD144+/lowCD36-CD146low). Sub-populations of endothelial cells co-expressed mesenchymal markers (CD90, CD26) suggesting a potential to undergo Endothelial to Mesenchymal Transition (EndMT). This EndMT was confirmed in vitro, where first trimester placental endothelial cells lost endothelial (CD31, CD34, CD144) and gained mesenchymal (CD90, CD26) marker expression even in endothelial differentiation conditions. In smooth muscle differentiation conditions, endothelial cells expressed α-SMA and calponin, showing further progression towards a contractile phenotype.

Differences in villous core cell heterogeneity over gestation reflect different stages of vascular development and organ growth. This work suggests that dysregulated EndMT could contribute to the increased perivascular:endothelial cell ratios in FGR, and in turn the increased vascular resistance seen in this pathology