Human placental vascular and perivascular cell heterogeneity differs between first trimester and term, and in pregnancies affected by foetal growth restriction.

Growth-restricted placentae have a reduced vascular network, impairing exchange of nutrients and oxygen. However, little is known about the differentiation events and cell types that underpin normal/abnormal placental vascular formation and function. Here, we used 23-colour flow cytometry to characterize placental vascular/perivascular populations between first trimester and term, and in foetal growth restriction (FGR). First-trimester endothelial cells had an immature phenotype (CD144+/lowCD36-CD146low), while term endothelial cells expressed mature endothelial markers (CD36+CD146+). At term, a distinct population of CD31low endothelial cells co-expressed mesenchymal markers (CD90, CD26), indicating a capacity for endothelial to mesenchymal transition (EndMT). In FGR, compared with normal pregnancies, endothelial cells constituted 3-fold fewer villous core cells (P < 0.05), contributing to an increased perivascular: endothelial cell ratio (2.6-fold, P < 0.05). This suggests that abnormal EndMT may play a role in FGR. First-trimester endothelial cells underwent EndMT in culture, losing endothelial (CD31, CD34, CD144) and gaining mesenchymal (CD90, CD26) marker expression. Together this highlights how differences in villous core cell heterogeneity and phenotype may contribute to FGR pathophysiology across gestation.