Background: The first trimester (T1) sees the establishment of oxygen-rich blood flow from maternal vessels into the placental intervillous space, and a consequent burst of oxidative stress. Cellular protective mechanisms involved in oxidative stress responses in T1 placenta are poorly understood. Nuclear factor (erythroid-derived-2)-like-2 (NFE2L2,or NRF2) is a transcription factor that binds Antioxidant Response Elements (AREs), providing cellular protection against oxidative stress by inducing phase II detoxification and antioxidant genes. Transcription of NFE2L2 and its target genes has not yet been described in T1 placenta. We aimed to determine the expression of NFE2L2 and target genes in early T1 (6-9w gestation, prior to onset of maternal blood-flow) and late T1 (10-12w gestation, during/after blood-flow onset).
Methods: Expression of NFE2L2 and the ARE containing genes HMOX1,NQO1,NQO2,FTL,FTH1, TXN,TXNRD1,GCLC,PRDX1,PRDX4,PRDX6, and GSTA3 was analysed using RNASeq data. As NFE2L2 is translocated to the nucleus upon activation, immunohistochemistry (IHC) was used to determine localisation in T1 placentas. Expression of NFE2L2 and target genes was also compared in a trophoblast microarray in HTR8/SVneo cultured in 1% oxygen, representing conditions before onset of maternal blood-flow, or 5%, representing placenta with blood-flow.
Results: Analysis of RNASeq data showed mean NFE2L2 expression was higher in late T1 placentas (91.0 counts per million; CPM,n=10) compared with early (73.7 CPM,P=0.048,n=20), but expression of ARE-containing genes did not differ. Neither NFE2L2, nor any ARE-containing genes, were differentially expressed in HTR8/SVneo in 1% vs. 5% oxygen. Preliminary IHC on 3 early and 7 late T1 placentas showed little or no trophoblast nuclear NFE2L2 staining at 6-8w. After 10w, cytotrophoblast and syncytiotrophoblast nuclei stained positive in 5 and 3 of 7 placentas, respectively.
NFE2L2 appears to be present in late T1 but since there were no corresponding changes in target gene expression, it may regulate different ARE-containing genes than those identified in other tissues.