Background: Preeclampsia (PE) is defined by the new onset of hypertension and proteinuria after 20 weeks of gestation, and affects 2 to 5% of pregnancies worldwide. PE is associated with iatrogenic preterm delivery, intrauterine growth restriction, placental abruption, and maternal morbidity and mortality. In PE, circulating maternal serum levels of soluble fms-like tyrosine kinase 1 (sFlt-1), oxidative stress and inflammation are increased. The histone acetyltransferase bromodomain protein (BRD)4 decompacts chromatin structures and remove nucleosomes to induce transcription of target genes. BRD4 is a master transcriptional regulator and has been implicated in cancer, obesity and inflammatory diseases.
Methods: BRD4 mRNA expression was assessed in preterm placenta from women with or without PE by qRT-PCR. BRD4 loss-of-function studies using siRNA or the chemical inhibitor JQ1 was performed in human placenta and in human umbilical vein endothelial cells (HUVECs). The effect of JQ1 and BRD4 siRNA knockdown on pro-inflammatory cytokines, chemokines, angiogenesis markers, adhesion molecules and oxidative stress were measured by qRT-PCR and ELISA.
Results: BRD4 mRNA expression is significantly increased in preterm PE placenta. JQ1 significantly reduced sFlt secretion from preterm PE placental explants under normoxic and hypoxic conditions. In primary trophoblast cells and HUVECs, TNF-α and hypoxic conditions upregulated the production of pro-inflammatory mediators (IL-6, IL-8, MCP-1, GROα), angiogenesis markers (sFlt, VEGFR) and adhesion molecules (ICAM-1) in primary trophoblast cells and HUVECs. Anti-oxidant status (eNOS) was also reduced in HUVECs. Treatment with the BRD4 inhibitor JQ1 or with BRD4 siRNA significantly reversed these effects in trophoblast cells and HUVECs.
Conclusion: Our findings demonstrate BRD4 to play an important role in propagating inflammation and endothelial dysfunction associated with PE in human placenta and HUVECs. Thus, these findings implicate blockade of BRD4 function may disrupt key pathways of the pathophysiology of PE.