Amelioration of Aberrant Glycosylation and the Maternal Adaptation to Pregnancy

Pregnancy is essential for survival but imposes considerable physiological stress on the mother. Maternal metabolism has to adapt to meet the needs of the growing fetus and to prepare for the postnatal demands of lactation. For example, food intake, heart rate, respiration and kidney glomerular filtration all rise. Adverse pregnancy outcomes (such as pre-eclampsia and fetal growth restriction) have life-long consequences for the health of mother and child. Preeclampsia affected ~14,000 women last year in England and such mothers have an eight-fold increased risk of heart disease. We do not know what the mechanism is for this.

The placenta grows during pregnancy to transfer nutrients, oxygen and waste products between mother and fetus. The placenta also orchestrates the necessary physiological changes in the mother by secreting a variety of hormones and proteins into the maternal circulation. The majority of proteins released from cells are made inside a cellular compartment - the endoplasmic reticulum (ER). As the newly synthesized proteins are folded in the ER they are further modified by addition of sugar side-chains, forming glycoproteins. The sugars are key to glycoprotein function and their clearance from circulation.

Placental dysfunction is implicated in numerous pregnancy disorders (such as pre-eclampsia and growth restriction), and a common feature of these is placental "ER stress". This stress is caused by a wide range of factors including malnutrition, low oxygen levels or infection and it perturbs ER function. We and others have reported that the structure of the sugar side-chains of glycoproteins secreted by cells suffering ER stress are changed or lost, with profound effects on protein function. For example, we have shown that vascular endothelial growth factor (VEGFA, a key factor stimulating blood vessel growth) is inactive if the sugar side-chains are altered by ER stress.

Thus, we hypothesise that the placental ER stress seen in complications of pregnancy may result in impaired maternal adaptations to pregnancy. In our pilot studies in which placental ER stress is increased, we see short-term effects on maternal physiology (reduced blood glucose and raised haematocrit) and altered metabolic signalling in the liver. Importantly and very surprisingly, we also found changes in an enzyme that modifies DNA structure (the process of DNA methylation) and which typically leads to long-term changes in gene function. This means that placental ER stress can induce changes in the maternal liver that would persist after pregnancy and potentially into later life. The biochemical and cellular mechanisms that underlie this effect are unknown and the work proposed here directly addresses this.

We will use our newly generated genetically modified mouse in which ER function is disrupted specifically in the placenta and nowhere else. We will characterise how ER stress changes the structure of the sugar side-chains on secreted placental proteins. These proteins normally regulate the function of the maternal liver and pancreas and mammary gland growth. We will determine whether the abnormally modified proteins are still active by collecting placental tissue and culturing it in the laboratory. We will use proteins released and specifically study the response of liver and pancreas cells to them. We will also assess mammary gland cell growth and the production of milk proteins and fat accumulation. Some of this work will be performed in mice as we need to study the relationship between changes in placental function and the maternal response.

Importantly, we will use a natural bile salt which we have shown reduces placental ER stress and we will determine whether it restores normal maternal physiology. This work will not only improve our understanding of the mechanisms underlying maternal adaptation to pregnancy but will determine whether this drug treatment has therapeutic potential in compromised pregnancies.

Pregnancy imposes considerable physiological stress on the mother and maternal metabolism has to adapt to this. The placenta orchestrates many of these changes. Adverse pregnancy outcomes (such as pre-eclampsia and fetal growth restriction) have life-long consequences for mother and child. Placental dysfunction is implicated in pregnancy disorders and a common feature is placental endoplasmic reticulum (ER) stress. This leads to perturbation of glycans on placental proteins and this has profound effects on their function and clearance. For example, we have shown that VEGFA fails to activate VEGFR2 if it's glycosylation is altered. Our pilot studies in which placental ER stress is increased, showed short term effects on maternal physiology and altered metabolic signalling in the maternal liver. Unexpectedly, hepatic DNA methyl transferase 3A also increased. Thus, placental ER stress has the potential to induce changes in maternal liver that persist after pregnancy and potentially into later life.

We will use our newly created junctional zone (Jz)-specific ER stress model (spongiotrophoblast specific Tpbpa-Cre crossed with floxed Perk mice). In a reduced oxygen environment, ablation of Jz Perk leads to ER stress and misglycosylation of secreted placental proteins. We will evaluate a wide range of maternal physiological, haematological, endocrine, biochemical, anatomical and molecular endpoints. Our preliminary data show that tauroursodeoxycholic acid (TUDCA) reduces placental ER stress. We will determine whether this treatment prevents the maternal maladaptation. We have established a Jz explant culture system and will identify, characterise and functionally test mis-glycosylated secreted placental proteins. We will determine how misglycosylated proteins affect target cells - derived from liver, pancreas and mammary gland. If the TUDCA treatment ameliorates the maternal maladaptation this may suggest a route toward therapeutic intervention.