During pregnancy, optimum maternal and fetal outcomes are determined by adequate nutrient partitioning between the mother and fetus. In turn, the placenta plays a critical role in nutrient partitioning during pregnancy, as it is responsible for secreting hormones that induce maternal insulin resistance and transports the nutrients available to support fetal growth and metabolic demand. Disturbances in placental endocrine function may lead to pregnancy complications such as gestational diabetes mellitus (GDM) and intrauterine growth restriction (IUGR) with immediate negative impacts on fetal outcomes. Moreover, as postulated by the Developmental Origins of Health and Disease (DOHaD) hypothesis, abnormalities in fetal nutrient supply and growth can programme the offspring to develop altered metabolic health in later life. Despite this, little is known about the role of the endocrine placenta in fetal nutrient supply, growth and the programming of adult metabolism. To study this, we conditionally disrupted the imprinting of the H19-Igf2 locus in the mouse placental endocrine zone (junctional zone, Jz; maternally inherited Jz-ICR1). This is because this locus is important in controlling the formation and function of placental endocrine cells. Thus, the aims of this study were 1) to assess the impact of Jz-ICR1Δ on placental morphology and materno-fetal nutrient supply and fetus growth 2) to evaluate how Jz-ICR1Δ impacts offspring metabolic health, both with a chow and an obesogenic postnatal diet 3) to determine the effect of Jz-ICR1Δ on the fetal hepatic transcriptome and evaluate whether these perturbations persist in the adult liver and relate to offspring metabolic phenotype. Fetal nutrient supply was determined in vivo and in vitro via placental substrate transport assays and quantifying nutrient transporter expression by qPCR respectively, whilst placental morphology was evaluated using histology and stereology techniques. Offspring metabolic health was evaluated via insulin and glucose tolerance tests, by examining pancreas morphology and insulin content, and by determining the abundance of proteins involved in gluconeogenesis, insulin signalling and lipid metabolism in the liver, skeletal muscle and white adipose tissue using Western blotting. RNA sequencing and bioinformatic analysis was used to assess changes in gene expression/functional pathways in fetal livers and select differentially expressed genes were quantified in adult offspring liver using qPCR.

The Jz-ICR1Δ mutation increased Jz volume at embryonic day (E) 16 (term ~E20), alongside an increase in Jz insulin-like growth factor 2 (Igf2) expression. Moreover, in response to Jz-ICR1Δ fetal growth was unaltered at E16 but reduced at E19. This was associated with a reduction in placental glucose transport to the fetus and a decrease in the surface area of the placenta for exchange on E16. Postnatally, Jz-ICR1Δ offspring displayed alterations in growth, adiposity, glucose and insulin handling and pancreatic function and morphology. This was also accompanied by changes in the abundance of proteins involved in gluconeogenesis, insulin signalling and lipid metabolism in offspring liver, skeletal muscle and white adipose tissue. However, these alterations were largely dependent on offspring sex and the postnatal diet consumed, with male offspring showing detrimental metabolic changes which were largely not present in females. In part, sex-dependent programmed changes in adult offspring metabolic phenotype appeared to be linked to sex-specific alterations in the fetal hepatic transcriptome on E19 in response to Jz-ICR1Δ, with a portion of genes displaying altered expression in the female fetus (G6pc, Rgs16) also tending to be altered in adult livers.

Overall, this study highlights the importance of the endocrine placenta in determining fetal nutrient supply and growth. Furthermore, defects in placental endocrine capacity programme changes in adult metabolic heath in a sex-dependent manner that appear to link to alterations in the fetal hepatic transcriptome. By improving our understanding of how the endocrine placenta leads to adverse fetal outcomes and the programming of offspring health, in future we may consequently lessen the burden of metabolic disease associated with gestational origins.