Various pregnancy complications, such as severe forms of preeclampsia or intrauterine
growth restriction, are thought to arise from failures in the differentiation of human
placental trophoblasts. Progenitors of the latter either develop into invasive extravillous
trophoblasts, remodeling the uterine vasculature, or fuse into multinuclear syncytiotrophoblasts
transporting oxygen and nutrients to the growing fetus. However, key regulatory factors
controlling trophoblast self-renewal and differentiation have been poorly elucidated.
Using primary cells, three-dimensional organoids, and CRISPR-Cas9 genome-edited JEG-3
clones, we herein show that YAP, the transcriptional coactivator of the Hippo signaling
pathway, promotes maintenance of cytotrophoblast progenitors by different genomic
mechanisms. Genetic or chemical manipulation of YAP in these cellular models revealed
that it stimulates proliferation and expression of cell cycle regulators and stemness-associated
genes, but inhibits cell fusion and production of syncytiotrophoblast (STB)-specific
proteins, such as hCG and GDF15. Genome-wide comparisons of primary villous cytotrophoblasts
overexpressing constitutively active YAP-5SA with YAP KO cells and syncytializing
trophoblasts revealed common target genes involved in trophoblast stemness and differentiation.
ChIP-qPCR unraveled that YAP-5SA overexpression increased binding of YAP-TEAD4 complexes
to promoters of proliferation-associated genes such as CCNA and CDK6 Moreover, repressive
YAP-TEAD4 complexes containing the histone methyltransferase EZH2 were detected in
the genomic regions of the STB-specific CGB5 and CGB7 genes. In summary, YAP plays
a pivotal role in the maintenance of the human placental trophoblast epithelium. Besides
activating stemness factors, it also directly represses genes promoting trophoblast
cell fusion.
