EGF Stimulates Proliferation in the Bovine Placental Trophoblast Cell Line F3 Via Ras and MAPK

In the bovine placenta, multinucleate trophoblast giant cells (TGC), evolving from uninucleate trophoblast cells, are crucial for feto-maternal interaction as they show endocrine activity and the ability to migrate and fuse with caruncular epithelial cells. In contrast to caruncular epithelial cells, the isolation and culture of bovine trophoblast cells is complicated because they cease to express their specific products, like placental lactogen (PL), during prolonged culture. In the present study, we aimed to establish a bovine cotyledonary trophoblast cell line targeting our long term goal to develop an in vitro model for the bovine placenta. Therefore, the functional activity of important signalling pathways was tested. Primary trophoblast cells were isolated from a bovine cotyledon of a male fetus and successfully subcultured and cryopreserved. The obtained cell line, termed F3, showed epithelial morphology and characteristic binuclear giant cells in small numbers through all passages. The trophoblastic origin of F3 cells was verified by amplification of a Y-chromosome specific DNA-sequence and the presence of PL mRNA. Immunofluorescence demonstrated that F3 cells were continuously positive for zonula occludens-2 (ZO-2), cytokeratin and vimentin, whereas they expressed the TGC specific marker PL only in the first two passages. F3 cell growth was accelerated in medium supplied with epidermal growth factor (EGF). EGF-stimulated proliferation was mediated through activation of Ras and the phosphorylation of mitogen-activated protein kinase (MAPK) 42 and 44. In conclusion, the F3 cell line shows several in vivo characteristics of bovine cotyledonary trophoblast cells. The response to EGF stimulation indicates that EGF plays a role during bovine placentation, and illustrated that F3 cells may provide a valuable tool for further mechanistic studies elucidating the feto-maternal interplay.