Amelioration of Aberrant Glycosylation and the Maternal Adaptation to Pregnancy

怀孕对生存至关重要，但对母亲造成相当大的生理压力。母体代谢必须适应胎儿生长的需要，并为产后哺乳的需要做好准备。例如，食物摄入量、心率、呼吸和肾小球滤过率都会上升。不良妊娠结局（如先兆子痫和胎儿生长受限）对母亲和儿童的健康具有终身影响。去年，英国约有14，000名妇女患有先兆子痫，这些母亲患心脏病的风险增加了8倍。我们不知道这是什么机制。胎盘在怀孕期间生长，在母亲和胎儿之间转移营养，氧气和废物。胎盘还通过分泌各种激素和蛋白质进入母体循环来协调母亲的必要生理变化。从细胞释放的大部分蛋白质在细胞隔室-内质网（ER）内产生。当新合成的蛋白质在ER中折叠时，它们通过添加糖侧链而进一步修饰，形成糖蛋白。这些糖是糖蛋白功能及其从循环中清除的关键。胎盘功能障碍与许多妊娠疾病（如先兆子痫和生长受限）有关，这些疾病的共同特征是胎盘“ER应激”。这种压力是由多种因素引起的，包括营养不良，低氧水平或感染，它扰乱了ER功能。我们和其他人已经报道了由遭受ER应激的细胞分泌的糖蛋白的糖侧链的结构改变或丢失，对蛋白质功能具有深远的影响。例如，我们已经证明，如果糖侧链被ER应激改变，血管内皮生长因子（VEGFA，刺激血管生长的关键因子）是无活性的，因此，我们假设在妊娠并发症中观察到的胎盘ER应激可能导致母体对妊娠的适应性受损。在我们的初步研究中，胎盘ER应激增加，我们看到对母体生理学的短期影响（血糖降低和红细胞压积升高）和肝脏代谢信号的改变。重要且非常令人惊讶的是，我们还发现了一种改变DNA结构（DNA甲基化过程）的酶的变化，这种酶通常会导致基因功能的长期变化。这意味着胎盘ER应激可以诱导母体肝脏的变化，这些变化在怀孕后持续存在，并可能持续到以后的生活中。这种效应背后的生化和细胞机制是未知的，这里提出的工作直接解决了这个问题。我们将使用我们新产生的转基因小鼠，其中ER功能被破坏，特别是在胎盘和其他地方。我们将探讨内质网应激如何改变分泌的胎盘蛋白糖侧链的结构。这些蛋白质通常调节母体肝脏和胰腺的功能以及乳腺的生长。我们将通过收集胎盘组织并在实验室中培养来确定异常修饰的蛋白质是否仍然具有活性。我们将使用释放的蛋白质，并专门研究肝脏和胰腺细胞对它们的反应。我们还将评估乳腺细胞生长和乳蛋白的产生以及脂肪积累。其中一些工作将在小鼠中进行，因为我们需要研究胎盘功能变化与母体反应之间的关系。重要的是，我们将使用一种天然胆汁盐，我们已经证明它可以降低胎盘ER应激，我们将确定它是否可以恢复正常的母体生理功能。这项工作不仅将提高我们对母体适应妊娠的机制的理解，而且将确定这种药物治疗是否对妊娠受损具有治疗潜力。

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.