Novel Molecular Mechanisms of Trophoblast Dysfunction Mediated by Imbalance between STOX1 Isoforms

Abstract

STOX1 is a transcription factor involved in two complex and frequent human diseases, preeclampsia and Alzheimer disease. However, precisely how STOX1 controls gene expression is still not well known. In this study, we identified binding sites of STOX1shared by the two major isoforms of the protein, STOX1A and STOX1B. Using newly generated villous trophoblast cell lines overexpressing either STOX1A or STOX1B, we identified a group of genes down-regulated by both isoforms, which contains one of the STOX1 binding sites that we identified in their promoters. Amongst those gene Annexin A1 (a major protein for membrane repair) was drastically down-regulated. We show that membrane repair was consistently abolished in BeWo cells overexpressing STOX1 isoforms. We then studied the effect of STOX on trophoblast fusion, a major event in villous trophoblast biology. STOX1A and B overexpression had opposite effects on trophoblast fusion: STOX1A accelerated the process and STOX1B prevented it in particular by deregulating syncytin genes which are endoretroviruses crucial for trophoblast fusion in mammals and other viviparous vertebrates. We also show that STOX1A overexpression led to abnormal regulation of oxidative and nitrosative stress in the cells. In sum STOX1 isoform imbalance appears as a possible cause of deregulation of gene expression in trophoblast, possibly leading to placental dysfunction and preeclampsia.