Convergence of MTOR and Glucocorticoid receptor signalling in the human placenta: effects of pre-term labour, nutrition and maternal stress

Abstract

A vital factor for foetal development is the nutrient transport at placental level. This is because any disturbances in the maternal compartments, for example due to maternal stress or nutritional status, which will affect foetal development, will involve the foetal-placental barrier. Moreover, numerous studies have linked other factors such as preterm labour as the leading cause of perinatal morbidity and mortality in the developed world. To this date, despite a numerous epidemiological and clinical studies that identify potential risk factors for the mother as well as the foetus, there is no comprehensive analysis at all these levels taken from the same cohort of patients. Our working hypothesis is that for a successful pregnancy certain events at nutritional, biochemical, genetic and molecular level could be tightly linked. Therefore, in this study we followed a “holistic” approach investigating how maternal stress, nutrition, placental mTOR and glucocorticoid receptor (GR) signalling can influence pregnancy outcome. We have decided to map in detail the components of these two signalling pathways as they appear to cross-talk as well as been implicated in stress responses. The largest part of the questionnaire was focused on the nutritional status with questions targeting the maternal dietary habits before, as well as during, pregnancy. The collection of data took place at the Department of Obstetrics and Gynecology, University of Crete Medical School. With regards to this profile, key findings included the significant reduction in the intake of alcohol, caffeine-containing and sugar-containing refreshments, whereas passive smoking during pregnancy stayed the same. Another major finding of this part of the study was the effects of maternal stress on foetal weight and how pregnancy planning was implicated in this complex relation. In our cohort, women with negative attitudes during pregnancy gave birth to infants with significantly lower birth weights (2.5Kg) than those women showing positive or neutral attitudes towards their pregnancy (2.9Kg). We then assessed how maternal stress might affect this signalling cascade using two placental models (BeWo and JEG-3 cell lines) mimicking a stress milieu in vitro. Treatment of these cell lines with cortisol (100nM and 1000nM) significantly downregulated Deptor and upregulated GAS5 at mRNA level. In an attempt to dissect further a potential gene-environment interaction, we have assessed how 4 well-characterised polymorphisms (ThtIII 1, Bcl I, ER22/23EK, N363S) of the GR gene might affect foetal and placental weight. We have demonstrated that only the maternal ThtIII 1 polymorphism was suggestive of a nature-nurture interaction since only in ThtIII 1 II (CC), maternal stress attitude predicts foetal weight-reduction, but not in ThtIII 1 (GC) independent of confounders such as BMI, pregnancy planning or fast food eating during pregnancy. This is the first time that a gene-environment interaction between a common GR polymorphism and foetal weight was noted. Finally, one of the most important findings of our study came from the preclinical studies using placental tissues. Quantitative PCR revealed that the major transcripts in the human placenta are GRα, GAS5 (decoy for GR DNA binding) and Deptor. We have shown for first time that there are marked differences in the relative mRNA abundance of these components between term and preterm labour as well as colocalisation of GRα with GAS5. With regards to placental regulation these data conclusively demonstrate that: a) there is evidence of gene-environment interaction between maternal stress, pregnancy planning, glucocorticoid receptor polymorphisms and foetal weight and b) potential cross-talk of mTOR and glucocorticoid signalling. We propose that measuring maternal stress levels in addition to circulating cortisol and mapping for known GR polymorphisms could become a useful non-invasive tool of diagnostic and prognostic value, with implications for preterm labour.