E-Poster Presentation ESA-SRB-ANZBMS 2021

Expression of transcription factor NR4A2 is not altered in placentas from cases of growth restriction or preeclampsia, but is reduced in hypoxic cytotrophoblast (#588)

Natasha de Alwis 1 2 , Sally Beard 1 2 , Natalie K Binder 1 2 , Natasha Pritchard 1 2 , Tu'uhevaha J Kaitu'u-Lino 1 2 , Sue P Walker 1 2 , Owen Stock 2 , Katie M Groom 3 , Scott Petersen 4 , Amanda Henry 5 , Joanne M Said 2 6 , Sean Seeho 7 , Stefan C Kane 2 8 , Stephen Tong 1 2 , Natalie J Hannan 1 2
  1. Mercy Perinatal, Mercy Hospital for Women, Melbourne, Victoria, Australia
  2. Department of Obstetrics and Gynaecology, University of Melbourne, Carlton, VIC, Australia
  3. Liggins Institute, University of Auckland, Auckland, New Zealand
  4. Centre for Maternal Fetal Medicine, Mater Mothers’ Hospital, Brisbane, Queensland, Australia
  5. School of Women’s and Children’s Health, UNSW Health, University of New South Wales, Sydney, New South Wales, Australia
  6. Maternal Fetal Medicine, Joan Kirner Women's & Children's Sunshine Hospital, Melbourne, Victoria, Australia
  7. The University of Sydney Northern Clinical School, Women and Babies Research, Sydney, New South Wales, Australia
  8. Department of Maternal Fetal Medicine, Royal Women's Hospital, Melbourne, Victoria, Australia

BACKGROUND: Nuclear Receptor Subfamily 4 Group A Member 2 (NR4A2; transcription factor) transcripts are elevated in the circulation of individuals whose pregnancies are complicated by preterm fetal growth restriction (FGR) and preeclampsia. In this study, we aimed to establish whether the increased transcripts originated from the dysfunctional placenta, and to uncover the function of placental NR4A2.

 

METHODS: NR4A2 mRNA expression was assessed in preterm and term placentas (qPCR). NR4A2 expression and protein was assessed in placenta from cases of preterm preeclampsia, FGR and preterm controls (qPCR and western blot). NR4A2 expression and protein was assessed in term placental explant tissue and primary cytotrophoblast exposed to hypoxia (1% O2 compared to 8% O2). Small interfering RNAs were used to silence NR4A2 in term primary cytotrophoblasts; expression of angiogenic, growth, apoptosis, inflammatory and oxidative stress genes were assessed. NR4A2 expression was assessed in a model of tumour necrosis factor (TNF)-α-induced endothelial dysfunction using primary human umbilical vein endothelial cells, and treatment of 200µM pravastatin.

 

RESULTS: NR4A2 expression was significantly higher in term compared to preterm placentas. NR4A2 mRNA expression and protein were not altered in placentas from preterm FGR or preeclamptic pregnancies. Hypoxia significantly reduced cytotrophoblast, but not placental explant NR4A2 expression. Silencing cytotrophoblast NR4A2 expression under hypoxia did not alter angiogenic Placental Growth Factor, nor anti-angiogenic sFlt-1 expression or protein secretion, but increased expression of cellular antioxidant, oxidative stress, inflammatory, and growth genes. Endothelial NR4A2 expression was not altered with TNF-α-induced dysfunction, or pravastatin treatment.

 

CONCLUSION: The origin of increased circulating NR4A2 transcripts in women with FGR and preeclampsia remains unknown. However, NR4A2 is downregulated in cytotrophoblast under hypoxic conditions, and its expression regulates several important cellular pathways. Further studies are required to identify whether these changes in placental NR4A2 are a protective mechanism, or a driver of placental dysfunction.