Extracellular adenosine mediated activation of the A2B adenosine receptor increases human syncytiotrophoblast formation.

Trophoblast fusion is crucial in developing multinucleated syncytiotrophoblast (STB) that form the placenta. Reports suggest that adenosine and adenosine triphosphate (ATP) plasma levels are elevated in preeclampsia compared to normal pregnant women. Plasma adenosine level is also reported to increase during normal gestation. In the cellular milieu, extracellular ATP is inflammatory, while adenosine has an immunosuppressive role. The present study provides evidence of the absolute requirement of cell-extracellular adenosine in STB reshaping. Under in-vitro conditions, fusion of the human choriocarcinoma cell line mimics the in-vivo syncytialization of placental villous cytotrophoblast cells. Cultured BeWo cells are committed to the placentogensesis pathway by being treated with forskolin (FSK), which forms multinucleated STB. Under culture conditions, cell extracellular adenosine boosts the STB formation process. Antagonists targeting CD39 (E-NTPDase1) and CD73 (ecto-5'-nucleotidase) modulate STB formation by preventing extracellular ATP dephosphorylation. Further scavenging extracellular adenosine by targeting adenosine deaminase (ADA) enzyme, STB formation accentuates by maintaining cell extracellular adenosine pool. Overall, this suggests CD39, CD73, and ADA activity are critical in maintaining normal STB formation. Further, a genetic knockdown approach and antagonist targeting A2B adenosine receptors (A2B-R) suppress STB formation, suggesting a specific role of cell-extracellular adenosine receptors during placenta development. Extracellular adenosine alone does not induce trophoblast differentiation, but its combination with FSK promotes robust STB formation, suggesting the promising role of extracellular adenosine during trophoblast fusion. These data suggest a potential role of the purinergic signalling pathway in maintaining the delicate balance of extracellular ATP and adenosine molecules regulating STB formation.