Dual Specificity Phosphatase 9 (DUSP9) Expression is Down-regulated in the Severe Pre-eclamptic Placenta

Objectives: Intrauterine growth restriction (IUGR) and pre-eclampsia are severe and clinically important manifestations of placental insufficiency. In the mouse, dual specificity phosphatase 9 (DUSP9) is critical to the normal development of the placenta, where knock-outs are growth restricted and have a placental phenotype similar to that seen in syndromes of human placental insufficiency. Our purpose was to characterize DUSP9 expression in normal human pregnancy and in cases of placental insufficiency.

Study Design: We used RT-PCR, immuno-histochemistry and Western blotting to characterize DUSP9 gene expression and protein levels across human gestation and in pregnancies complicated by severe IUGR and/or severe pre-eclampsia. DUSP9 promoter methylation was studied in pathologic and pre-term control placentas to investigate potential epigenetic regulation. First trimester villous explants and BeWo cells were treated with DUSP9 silencing RNA to determine the effect on downstream pathways. Placental hypoxia is a hallmark of pre-eclampsia; therefore explants were subjected to hypoxic culture conditions to determine the effect of oxygen on DUSP9 expression in vitro.

Results: DUSP9 expression was evident in villous trophoblast and declined during development. DUSP9 protein was significantly lower in severe pre-eclamptic placentas compared to severe growth restriction. This was not epigenetically mediated by promoter hyper-methylation, and the downstream pathway ERK1/2 was not significantly affected. DUSP9 expression in first trimester explants was significantly decreased by 74 ± 20% in hypoxic (3% oxygen) culture conditions. In BeWo cells and explanted placental villi treated with DUSP9 silencing RNA, expression of DUSP9 was down-regulated by 61% and 62% respectively. There was a trend to increased phosphorylation of the downstream target ERK1/2 in DUSP9 down-regulated BeWo cells and explanted placental villi.

Conclusion: DUSP9 protein levels were markedly suppressed in severe pre-eclampsia, but not in severe IUGR. This suppression might be attributable to the prolonged hypoxic conditions found in pre-eclampsia.