Decreased expression and activation of Stat3 in severe preeclampsia

Severe preeclampsia (PE) is a major cause of maternal mortality and morbidity worldwide. Signal transducer and activator of transcription 3 (Stat3) signal pathway can modulate various fundamental cellular processes. However, whether Stat3 plays a role in the pathogenesis of severe PE is unknown. Therefore, in this study, the expression levels of Stat3 pathway-related genes and proteins, Stat3, pStat3, IL-6, Mcl-1L, Bcl-xL, survivin, MMP-2, and MMP-9, were evaluated by immunohistochemistry (IHC), Western blot analysis and real-time PCR in the severe preeclamptic placentas. Our results showed that Stat3 and pStat3 immunoreactivity were localized in both extravillous cytotrophoblast cells and villous trophoblast cells in the placentas. As compared with normotensive pregnancies, significantly decreased expressions of Stat3 and pStat3 proteins were observed in extravillous cytotrophoblast cells, villous trophoblast cells and entire placentas in patients with severe PE. The expression levels of Stat3, IL-6, survivin and MMP-2 mRNA were significantly decreased in severe preeclamptic placentas, while Mcl-1L, Bcl-xL and MMP-9 mRNA levels were unchanged. IHC results further confirmed that there was a significant decrease of IL-6, survivin and MMP-2 proteins expression in the severe preeclamptic placentas compared with the normal specimens. These findings suggested that decreased expression and activation of the Stat3 may be caused by decreased expression of a Stat3 upstream gene, such as IL-6. Decreased Stat3 expression and activation may play an important role in the pathogenesis of PE through regulation of the transcription of the Stat3 targeted genes survivin and MMP-2 to modulate apoptosis and invasion of placental trophoblastic cells.