Sterol Metabolism During Pregnancy and Development

胎儿获取甾醇对发育和生长至关重要。胎儿有两种可能的胆固醇来源：新生合成和外源性固醇。如果没有这些来源所需的胆固醇，胎儿将无法存活或发育异常。在我们之前的资助期间获得的数据表明，除了来自新生合成的胆固醇外，胎儿还从母体循环中获得胆固醇。母源性固醇的增加似乎依赖于胚胎外胎儿组织中的固醇平衡，这些组织保护胎儿免受母体循环成分、胎盘和卵黄囊的直接接触。因此，目前提出的假设是：1)胎儿从母体循环中获得胆固醇；2)胎儿体内的母体胆固醇具有代谢活性。有4个具体的目标来检验这些假设。首先，从母体循环中获得的胆固醇量将被量化。为了描述所涉及的过程，将使用不同发育阶段的不同脂蛋白和不同的母体血浆胆固醇浓度来检查运输。与胎儿发育有关的特定蛋白质的作用也将在缺乏这些蛋白质的转基因动物身上进行研究，比如巨噬蛋白。其次，将评估从胎盘中摄取、运输和分泌胆固醇的过程。这些研究将在人源性癌滋养细胞系和人胎盘灌注中完成。为了检验这一过程，我们将研究脂蛋白（LDL和HDL）、细胞胆固醇和脂质受体（低脂apoAI和磷脂囊泡）浓度增加的影响。第三，将在卵黄囊器官培养中测定卵黄囊分泌脂蛋白的效应物。蛋黄囊中的胆固醇和甘油三酯浓度和甘油三酯组成将被控制，由此对脂蛋白分泌产生的影响将被检查。特定蛋白质在这一过程中的作用也将被研究。最后，将在母体积累了不同数量胆固醇的胎儿组织中研究涉及固醇平衡的蛋白质加工、固醇调节元件结合蛋白和Sonic hedgehog（一种参与前脑模式的蛋白质）的激活。基于这一建议的结果，我们期望确定新的方法来增强外源性胆固醇在发育中的胎儿或胚胎中的呈现。

The acquisition of sterol by the fetus is essential for development and growth. The fetus has two potential sources of cholesterol, de novo synthesis and exogenous sterol. Without the required amount of cholesterol from these sources, the fetus will not survive or will develop abnormally. Data obtained during our previous funding period suggests that the fetus acquires cholesterol from the maternal circulation in addition to that derived from de novo synthesis. The accretion of maternal- derived sterol seems to be dependent upon the sterol balance in the extra-embryonic fetal tissues that protect the fetus from direct contact with circulating maternal constituents, the placenta and yolk sac. Thus, the hypotheses for the present proposal are 1) that the fetus acquires cholesterol from the maternal circulation and 2) that the maternal cholesterol within the fetus is metabolically active. There are 4 specific aims which will test these hypotheses. First, the amount of cholesterol acquired from the maternal circulation will be quantitated. To delineate the processes involved, transport will be examined using different lipoproteins at different stages of development and with varied maternal plasma cholesterol concentrations. The role of specific proteins that have been implicated in fetal development will also be examined in genetically altered animals lacking the proteins in question, such as megalin. Second, the processes involved in the uptake, transport and secretion of cholesterol from the placenta will be evaluated. These studies will be completed in a human derived carcinoma trophoblastic cell line and in human placental perfusions. To examine the processes, we will study the effects of increasing concentrations of lipoproteins (LDL and HDL), cellular cholesterol and lipid acceptors (lipid-poor apoAI and phospholipid vesicles). Third, the effectors of lipoprotein secretion from the yolk sac will be determined in a yolk sac organ culture. Cholesterol and triglyceride concentrations and triglyceride composition will be manipulated in the yolk sacs and the resultant effect this has on lipoprotein secretion will be examined. The role of specific proteins in this process will also be examined. Finally, the processing of proteins involved in sterol balance, the sterol regulatory element binding proteins, and the activation of Sonic hedgehog, a protein involved in patterning of the forebrain, will be studied in fetal tissues that have accrued different amounts of maternal cholesterol. Based on the results of this proposal, we expect to define new approaches to enhance the presentation of exogenous cholesterol to the developing fetus or embryo.