Signalling Pathways of Oestrogen-Related Receptor Gamma (ESRRG) in Pregnancies complicated by Fetal Growth Restriction

Abstract

Fetal growth restriction (FGR), when a fetus does not achieve its growth potential, affects 10% of pregnancies in high-income countries. FGR is not only associated with increased risk of perinatal morbidity and mortality, but also increases the possibility of cardiovascular diseases or metabolic disorders in later life. To date, there is no effective method to prevent or treat FGR, except delivery of the infant. Understanding the underlying mechanisms responsible may help to develop therapies to prevent or treat the condition. FGR is associated with placental dysfunction, which has been attributed to various causes, including: hypoxic conditions in later pregnancy, prenatal exposure to the environmental contaminant BPA, and altered levels of some miRNAs. Reduced levels of oestrogen-related receptor gamma (ESRRG), a nuclear receptor highly expressed in the normal human placenta, is also observed in placentas complicated by FGR. Restoring ESRRG function may improve placental function, but the mechanisms regulating ESRRG signalling are currently not fully understood. This thesis assessed whether hypoxia, BPA exposure and miRNAs modulate ESRRG signalling pathways, and explored whether this signalling pathway contributes to the abnormal cell turnover and hormone secretion that are features of FGR placentas. The programme of research had three aims: 1) To determine the role of ESRRG signalling pathways in FGR pregnancies and to assess whether hypoxia can regulate ESRRG expression and signalling in a cultured placental explant model. Placentas from FGR pregnancies and from pregnancies with appropriately grown infants were collected. ESRRG mRNA and protein expression were decreased in FGR placentas; this was accompanied by a reduction in mRNA expression of several downstream genes. The impact of hypoxia on ESRRG was then determined using placental explants from term healthy placentas cultured in 1% O2, 6% O2, 21% O2 or treated with cobalt chloride (200µM, CoCl2) for four days of culture. The mRNA expression of ESRRG and its downstream genes were decreased in the explants cultured in 1% O2 or treated with CoCl2, with a reduced percentage of cells in cycle and an increase in apoptotic cells. Application of the ESRRG agonist, DY131, rescued abnormal cell turnover via restoring ESRRG signalling in the hypoxic placental explants. 2) To assess the impact of BPA on ESRRG signalling pathways, placental explants from 18 healthy term placentas (9 female and 9 male) were exposed to BPA (1pM-1µM) for up to 48 hours of culture. ESRRG mRNA levels were significantly increased in the explants treated with 1µM BPA for 24 hours. ESRRG signalling was sex-specific: down-regulation of ESRRG mRNA and protein expression in male placentas and up-regulation of ESRRG signals in female placentas was observed. BPA treatment did not alter hCG secretion, but induced LDH release from the female placentas with 1pM BPA exposure. Physiological BPA exposure did not alter the percentage of cells in cycle or apoptotic cells. 3) To establish if the ESRRG signalling pathway is modulated by miR-377. Normal term placental explants were treated with miR-377 mimics to overexpress miR-377. ESRRG mRNA and protein expression were significantly decreased in these explants, but there was no alteration in the expression of ESRRG‘s downstream genes. miR-377 overexpression also reduced the numbers of cells in cycle and the percentage of apoptotic cells. miR-377 RNA expression was comparable between FGR and AGA placentas. The exact regulatory relationship between miR-377 and ESRRG is still unknown and whether miR-377 directly regulates ESRRG needs to be determined in future work.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Lynda Harris (Supervisor), Alexander Heazell (Supervisor) & Karen Forbes (Supervisor)