Amelioration of Aberrant Glycosylation and the Maternal Adaptation to Pregnancy

怀孕是生存的关键，但也会给母亲带来相当大的生理压力。母亲的新陈代谢必须适应不断增长的胎儿的需要，并为出生后哺乳的需求做好准备。例如，食物摄入量、心率、呼吸和肾小球滤过率都会增加。不良妊娠结局(如先兆子痫和胎儿生长受限)会对母婴健康造成终生后果。去年，英国约有1.4万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。胎盘还通过将各种激素和蛋白质分泌到母亲的血液循环中来协调母亲必要的生理变化。从细胞中释放的大部分蛋白质是在一个细胞隔间--内质网(ER)内制造的。当新合成的蛋白质在内质网中折叠时，它们会被添加糖侧链进一步修饰，形成糖蛋白。糖是糖蛋白功能和清除循环的关键。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，这些疾病的一个共同特征是胎盘“内质网应激”。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，它扰乱了内质网的功能。我们和其他人已经报道，受到内质网应激的细胞分泌的糖蛋白的糖侧链结构发生改变或丢失，对蛋白质功能产生深远影响。例如，我们已经证明，如果内质网应激改变糖侧链，血管内皮生长因子(VEGFA，刺激血管生长的关键因素)是无效的。因此，我们假设妊娠并发症中出现的胎盘内质网应激可能导致母亲对怀孕的适应能力受损。在我们的初步研究中，胎盘ER应激增加，我们看到了对产妇生理的短期影响(降低血糖和升高红细胞压积)，并改变了肝脏的代谢信号。重要且非常令人惊讶的是，我们还发现了一种修改DNA结构(DNA甲基化过程)的酶的变化，这种变化通常会导致基因功能的长期变化。这意味着胎盘内质网应激可以诱导母亲肝脏的变化，这种变化将在怀孕后持续，并可能持续到以后的生活。这种效应背后的生化和细胞机制尚不清楚，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，在这种小鼠中，ER功能特别是在胎盘中被破坏，而不是在其他地方。我们将描述内质网应激如何改变分泌的胎盘蛋白上糖侧链的结构。这些蛋白质通常调节母亲的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培养来确定异常修饰的蛋白质是否仍然有效。我们将使用释放的蛋白质，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的生长以及乳蛋白和脂肪的积累。其中一些工作将在小鼠身上进行，因为我们需要研究胎盘功能变化和母体反应之间的关系。重要的是，我们将使用一种我们已经证明可以减少胎盘ER压力的天然胆盐，我们将确定它是否能恢复正常的母体生理。这项工作不仅将提高我们对孕妇适应妊娠的潜在机制的理解，还将确定这种药物治疗对不良妊娠是否具有治疗潜力。

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.