Expression pattern and function of Notch2 in different subtypes of first trimester cytotrophoblast

Notch signalling has been shown to control cytotrophoblast (CTB) proliferation, differentiation and motility suggesting that the conserved signalling pathway could be critical for human placental development. Since individual Notch receptors have not been elucidated, we herein investigated expression pattern and function of Notch2 in different first trimester trophoblast subpopulations.

Localisation of Notch2 was analysed in first trimester placental and decidual tissues using immunofluorescence. Notch2 transcript and protein levels were studied by qRT-PCR and Western blotting in proliferative EGF receptor (EGFR)(+) and differentiated HLA-G(+) CTBs, respectively, isolated from early placentae by MACS. CTB migration through fibronectin-coated transwells as well as proliferation (EdU labelling) in floating villous explant cultures and primary CTBs were investigated in the presence of Notch2 siRNAs or specific antibodies blocking Notch2 cleavage.

In tissue sections Notch2 expression was higher in HLA-G(+) distal cell column trophoblasts (dCCTs) compared to proximal CCTs. Accordingly, expression of Notch2 mRNA and protein were elevated in isolated HLA-G(+) CTBs compared to EGFR(+) CTBs. Notch2 was also detectable in interstitial CTBs as well as in intramural CTBs associated with maternal decidual vessels. Antibody-mediated inhibition of Notch2 signalling did not affect proliferation, but increased migration of SGHPL-5 cells and primary CTBs. Similarly, Notch2 siRNA treatment promoted trophoblast motility.

Notch2 is present in differentiated cells of the extravillous trophoblast lineage, such as dCCTs, interstitial and intramural CTBs, suggesting diverse roles of the particular receptor. Notch2 signalling, activated by cell-cell contact of neighbouring dCCTs, could attenuate trophoblast migration.