Background: During the first trimester of human pregnancy extravillous trophoblasts (EVTs) grow out from anchoring villi, invade the decidualised endometrium and remodel the uterine spiral arteries. Inadequate EVT invasion is associated with pregnancy complications including intra-uterine growth restriction (IUGR) and pre-eclampsia.  During the first trimester, the placenta exists in a physiologically normal low oxygen (1-2%) environment, which may be important in regulating EVT outgrowth formation and expansion. The oxygen responsive transforming growth factor beta (TGFβ) family of cytokines have been suggested to regulate EVT outgrowth. This work aimed to quantify the effects of TGFβ1, β2 and β3 on EVT outgrowth from first trimester villous explants.

Methods: Exogenous TGFβ1, β2 and β3 were added to a quantitative 2-dimensional first trimester villous explant model and the frequency and area of EVT outgrowth was determined. EVTs isolated from first trimester placentae were cultured in environments containing 8% or 1.5% oxygen and the concentration of TGFβ2 and 3 in the conditioned medium was determined by ELISA.

Results: No significant difference in the frequency of EVT outgrowth between explants treated with TGFβ1, β2 or β3 was observed.  However, treatment with TGFβ2, but not β1 or β3, resulted in a significantly smaller area of EVT outgrowth (p=0.03, n=6).  There was no significant difference in the secretion of TGFβ2 or 3 from isolated primary EVTs cultured in 1.5% or 8% oxygen.

Conclusions: TGFβ1, 2 or 3 do not affect the frequency of EVT outgrowth formation, indicating that they do not promote cytotrophoblast differentiation into EVTs. TGFβ2 inhibits EVT outgrowth expansion from first trimester villi, but as oxygen tension did not alter the secretion of TGFβ2 by EVTs, this inhibition of outgrowth expansion is unlikely to be mediated by the low oxygen conditions in early pregnancy.