Sterol Metabolism During Pregnancy and Development

胎儿获取甾醇对发育和生长至关重要。 胎儿胆固醇有两个潜在来源，从头合成和外源性固醇。 如果没有来自这些来源的所需量的胆固醇，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，胎儿除了从从头合成中获得胆固醇外，还从母体循环获得胆固醇。 母体来源的甾醇的增加似乎取决于胚胎外胎儿组织中的甾醇平衡，该组织保护胎儿免于与循环母体成分、胎盘和卵黄囊直接接触。 因此，本建议的假设是：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。 有四个具体目标将测试这些假设。 首先，将定量从母体循环中获得的胆固醇的量。 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转运。 与胎儿发育有关的特定蛋白质的作用也将在缺乏相关蛋白质（如巨蛋白）的转基因动物中进行研究。 其次，将评估胎盘中胆固醇的摄取、运输和分泌过程。 这些研究将在人源性癌滋养层细胞系和人胎盘灌注中完成。 为了研究这些过程，我们将研究脂蛋白（LDL和HDL）、细胞胆固醇和脂质受体（脂质贫乏的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确定从卵黄囊分泌脂蛋白的效应物。 将在卵黄囊中操作胆固醇和甘油三酯浓度以及甘油三酯组成，并检查其对脂蛋白分泌的影响。 还将研究特定蛋白质在这一过程中的作用。 最后，参与固醇平衡的蛋白质的加工，固醇调节元件结合蛋白，以及参与前脑模式化的蛋白质Sonic hedgehog的激活，将在已经积累了不同量的母体胆固醇的胎儿组织中进行研究。 基于这一提议的结果，我们期望定义新的方法来增强外源性胆固醇对发育中的胎儿或胚胎的呈递。

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.