Sterol Metabolism During Pregnancy and Development

胎儿获得类固醇对于发育和生长是必不可少的。胎儿有两个潜在的胆固醇来源，即从头合成和外源性类固醇。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，胎儿除了从从头合成中获得胆固醇外，还从母体循环中获得胆固醇。母体来源的类固醇的增加似乎依赖于胚胎外胎儿组织中的类固醇平衡，这些组织保护胎儿免受与循环中的母体成分、胎盘和卵黄囊的直接接触。因此，本提议的假设是1)胎儿从母体循环中获得胆固醇，2)胎儿内的母体胆固醇在代谢上是活跃的。有四个具体的目标将检验这些假设。首先，从母体循环中获得的胆固醇的数量将被量化。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转运。还将在缺乏相关蛋白质的转基因动物身上研究特定蛋白质在胎儿发育中的作用，例如巨蛋白。其次，将评估与胎盘胆固醇的吸收、运输和分泌有关的过程。这些研究将在人类来源的癌症滋养细胞系和人类胎盘灌注液中完成。为了研究这一过程，我们将研究脂蛋白(低密度脂蛋白和高密度脂蛋白)、细胞胆固醇和脂质受体(低脂蛋白ApoAI和磷脂小泡)浓度增加的影响。第三，卵黄囊脂蛋白分泌的影响因素将在卵黄囊器官培养中确定。胆固醇和甘油三酯的浓度和甘油三酯的组成将在卵黄囊中受到控制，由此产生的对脂蛋白分泌的影响将被检测。还将研究特定蛋白质在这一过程中的作用。最后，将在积累了不同数量的母体胆固醇的胎儿组织中，研究参与类固醇平衡的蛋白质的处理，以及参与前脑模式形成的Sonic Hedgehog的激活。基于这一建议的结果，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.