Jumonji domain containing protein 6 is decreased in human preeclamptic placentas and regulates sFLT-1 splice variant production

The anti-angiogenic protein, soluble fms-like tyrosine kinase-1 (sFLT-1), plays a central role in preeclamptic pathophysiology. A splice variant of FLT-1 (VEGF receptor 1), sFLT-1 is released in excessive amounts from the preeclamptic placenta into the maternal circulation, where it causes endothelial dysfunction manifesting as end-organ disease. However, the mechanisms regulating its production within the placenta remain poorly understood. Recently it was shown in endothelial cells that Jumonji domain containing protein 6 (JMJD6) hydroxylates U2 small nuclear ribonucleoprotein auxiliary factor 65-kDa subunit (U2AF65, a component of the splicesome). The hydroxylation by JMJD6 is oxygen dependent. Under hypoxia, JMJD6 is less able to hydroxylate U2AF65, and this unhydroxylated form of U2AF65 biases splicing of FLT-1 to sFLT-1. We assessed whether oxygen-sensing JMJD6 is differentially expressed in preeclamptic placenta and regulates sFLT-1 splicing in placenta via U2AF65. JMJD6 protein expression was significantly reduced in preterm preeclamptic placenta (P <, 0.0001; n = 21) relative to preterm controls (n = 10). Exposing both placental and endothelial cells to hypoxia significantly reduced JMJD6 mRNA and increased sFLT-1 mRNA and protein expression. Silencing JMJD6 in primary endothelial and trophoblast cells significantly increased sFLT-1 secretion. Next, we examined whether these molecules may be directly interacting. We demonstrated that placental U2AF65 colocalized with JMJD6. In turn, we found JMJD6 directly interacts with U2AF65, which in turn produces sFLT-1 mRNA transcripts. Taken together, our findings provide evidence that JMJD6 may play a role in regulating the production of sFLT-1 in the preeclamptic placenta. Decreased placental JMJD6 expression may be an important component to the pathophysiology of preeclampsia.