Preeclampsia, a major cause of maternal and perinatal morbidity and mortality, is thought to be attributable to dysregulation of trophoblast invasion and differentiation. Microarray studies have shown that triggering receptor expressed on myeloid cells (TREM) 1, a cell surface molecule involved in the inflammatory response, is increased in preeclamptic placentas. The aim of this study was to determine the level of TREM-1 expression in severe early-onset preeclamptic placentas and its functional role in trophoblast differentiation. Placenta was obtained from women with severe early-onset preeclampsia (n = 19) and gestationally matched preterm controls placentas (n = 8). The TREM-1 expression was determined by quantitative reverse transcriptase polymerase chain reaction and Western blotting. The effect of TREM-1 small interfering RNA on cell fusion and differentiation was assessed in BeWo cells. The effect of oxygen tension on TREM-1 levels, in basal or forskolin-treated BeWo cells, was also assessed. The TREM-1 was localized to the syncytiotrophoblast layer, and TREM-1 messenger RNA and protein expression was significantly increased in preeclamptic placentas. The BeWo cells treated with forskolin were associated with increased TREM-1 expression. The TREM-1 knockdown inhibited forskolin-induced expression of the differentiation marker β-human chorionic gonadotropin but had no effect on the cell-fusion marker E-cadherin. The increase in TREM-1 expression in BeWo cells treated with forskolin during normoxic conditions was reduced in forskolin-treated cells under hypoxic conditions. In conclusion, TREM-1 is increased in preeclamptic placentas and by forskolin treatment. Knockdown of TREM-1 by RNA interference inhibits cell differentiation but has no effect on cell–cell fusion. Finally, we show that TREM-1 upregulation is attenuated under hypoxic conditions in which cell differentiation is impaired.
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