POTOCYTOSIS AND PLACENTAL TRANSPORT FUNCTION

当前项目的目标是获得一个清晰的理解 关于叶酸从母体转移到胎儿的机制， 胎儿正常生长发育所必需的营养物质- 胎盘单位。叶酸在胎儿发育中的重要作用是 最近的研究结果强调，在治疗过程中补充维生素 围孕期降低神经管的发生率 胎儿发育中的缺陷。胎儿对营养的需求 叶酸只能通过母亲的胎盘转移来满足。 因此对分子机制有了透彻的了解 参与这一过程是有根据的。叶酸在土壤中的运输 胎盘的形成有两个步骤--从母体体内进入叶酸 通过面向母体的刷子进入合体滋养细胞的循环 边缘膜和叶酸从合体滋养层细胞排入 胎儿隔室横跨面向胎儿的基底膜。有建议说 第一步，即进入合体滋养层细胞，利用 一种新的细胞途径，称为细胞增多症。根据建议的 模型中，这一途径涉及被称为小窝的独特的膜结构 并且使得三个分子组分之间能够有效地偶联 参与叶酸进入，即V型H+泵，叶酸受体， 和叶酸转运蛋白。叶酸受体的功能是 从母体循环中捕获叶酸并将其浓缩到 小窝。叶酸转运体将叶酸从肺泡中转运出来。 空间进入细胞质，这一过程由一种 跨膜H+梯度。H+泵的作用就是产生这个 驱动力。该模型的实验支持将通过以下方式获得 表征这些成分的分子和功能性质 通过演示组件与凹凸体的共局域化， 小凹病毒特异的蛋白质，在刷状缘膜中 合体滋养层细胞。叶酸受体和叶酸转运蛋白 从人胎盘中克隆的cDNA及其可用性 促进拟议的研究。它们的功能特征 克隆的蛋白质将通过表达各自的cDNA来进行 在没有或很少内源性叶酸受体的哺乳动物细胞中 或叶酸转运体。叶酸转运蛋白的基因一直是 定位于人类染色体21q22.3，一个被认为是关键的区域 唐氏综合征(三体)的发病机制及临床特点 21)。建议进行研究以阐明其结构和组织 叶酸转运蛋白基因。叶酸交叉的机制 基底膜尚不清楚。很可能是叶酸 转运蛋白也在这个膜上表达，促进了细胞的退出 进程。拟议的研究将描述运输机制。 可用于分离的基底膜囊泡中的叶酸，还 确定叶酸在合体滋养层细胞内的代谢命运。 培养的滋养层细胞和绒毛膜癌细胞将作为 研究叶酸转运调控的模型系统 胎盘受激素、叶酸供应和酒精的影响。

The objective of the current project is to obtain a clear understanding of the mechanisms involved in the maternal-to-fetal transfer of folate, an essential nutrient for normal growth and development of the feto- placental unit. The essential role of folate in fetal development is underscored by recent findings that supplementation of the vitamin during the periconceptional period decreases the incidence of neural tube defects in developing fetus. The nutritional needs of the fetus for folate have to be met solely by transplacental transfer from the mother and therefore a thorough understanding of the molecular mechanisms involved in this process is warranted. Transport of folate across the placenta occurs in two steps - entry of folate from the maternal circulation into the syncytiotrophoblast across the maternal-facing brush border membrane and exit of folate from the syncytiotrophoblast into the fetal compartment across the fetal-facing basal membrane. It is proposed that the first step, i.e. entry into the syncytiotrophoblast, utilizes a novel cellular pathway called potocytosis. According to the proposed model, this pathway involves unique membrane structures known as caveolae and enables an efficient coupling among the three molecular components participating in folate entry, namely V-type H+ -pump, folate receptor, and folate transporter. The function of the folate receptor is to capture folate from the maternal circulation and concentrate it in caveolae. The folate transporter transports folate from the caveolar space into the cytoplasm, and this process is energized by a transmembrane H+ gradient. The role of the H+ - pump is to generate this driving force. Experimental support for the model will be obtained by characterizing the molecular and functional nature of these components and by demonstrating colocalization of the components with caveolin, the caveola-specific protein, in the brush border membrane of the syncytiotrophoblast. The folate receptor and the folate transporter have been cloned from human placenta and the availability of the cDNAs facilitates the proposed studies. Functional characterization of these cloned proteins will be carried out by expressing the respective cDNAs in mammalian cells which possess no or little endogenous folate receptor or folate transporter. The gene for the folate transporter has been localized to human chromosome 21q22.3, a region believed to be critical in the pathogenesis of the clinical features of Down Syndrome (Trisomy 21). Studies are proposed to elucidate the structure and organization of the folate transporter gene. The mechanisms by which folate crosses the basal membrane are not known. It is likely that the folate transporter is also expressed in this membrane, facilitating the exit process. Proposed studies will characterize the transport mechanism available for folate in isolated basal membrane vesicles and also determine the metabolic fate of folate within the syncytiotrophoblast. Cultured trophoblast cells and choriocarcinoma cells will be used as model systems to investigate the regulation of folate transport in placenta by hormones, folate availability and alcohol.