StarD7 a fusogenic protein in trophoblasts

ANGELETTI SOFÍA; CHEN Q; PEARSON SM; GENTI-RAIMONDI SUSANA; CHAMLEY L

Adelaide, Australia

Congreso; International Federation of Placenta Associations Meeting; 2009

International Federation Placenta Associations

StarD7 is a novel protein of unknown function that belongs to the STARTlipid domain family and is expressed in the cytoplasm of human trophoblast cells. It was previously found that StarD7 is able to interact with phosphatidylserine. We have previously shown that StarD7 is partially relocated from the cytoplasm to the plasma membrane during in vitro cytotrophoblast differentiation into syncytiotrophoblast. This study further investigates the function of StarD7 in trophoblasts. MTT-based cell proliferation assays were preformed in triplicate using BeWo cells that were incubated with increasing concentrations of recombinant StarD7 protein (0, 5, 10 or 20 mg/ml). Cell viability was determined by propidium iodide staining and detection of LDH in the culture supernatants. Statistical analysis was by t-test and a P value < or ¼ 0.05 was considered to be significant. Syncytialization of BeWo cells was assessed by immunostaining for desmoplakin. The proliferation of BeWos was significantly inhibited by incubation with StarD7 at 5, 10 and 20 mg/ml. Incubation of BeWos with StarD7 did not cause a significant increase in cell death as measured by either propidium iodide or LDH release at any of the concentrations we tested. Fluorescent microscopy suggested that there were few intracellular desmosomes between adjacent BeWo cells after treatment with StarD7 at 20 mg/ml. BeWo cultures treated with StarD7 at these concentrations had similar levels of intracellular desmosomes to those found in control cultures treated with 5 mM forskolin. These results together demonstrate that exogenous Star D7 causes BeWo cells to cease proliferating but does not cause their death. The reduction in desmosomes indicates loss of intracellular boundaries leading us to conclude that StarD7 can initiate/facilitate the syncytialization of BeWo cells. Our results suggest that the phospholipid-binding protein StarD7 may play a physiological role during the differentiation of cytotrophoblasts into syncytiotrophoblast. Keywords: START lipid domain, Trophoblast proliferation arrest, Syncytialization, Cell fusion