Mechanisms & Significance of Cubilin-Mediated HDL Uptake.

描述（由申请方提供）：Cubilin是一种外周膜蛋白，与其共受体巨蛋白一起介导卵黄囊内脏内胚层（VE）和肾近端小管中高密度脂蛋白（HDL）的内吞作用。cubilin介导的HDL摄取对胚胎发育以及成人生理的意义尚不清楚。在发育过程中，假设cubilin活性对于胚胎获得支持胚胎发生所需的母体HDL相关胆固醇、磷脂、甘油三酯和/或脂溶性维生素至关重要。卵黄囊cubilin的重要作用是由严重的发育异常时，观察到的cubilin抗体给药妊娠大鼠或子宫外培养的胚胎。在成人生理学中，假设HDL的肾cubilin/megalin摄取参与影响血液中HDL稳态水平的反馈机制。支持这一假设来自我们的研究结果，肾巨蛋白活性的条件性缺乏导致血浆HDL的增加。为了检验上述假设，并表征cubilin功能的基本机械特征，提出了三个具体目标。第一个目的是表征cubilin基因靶向缺失的纯合和杂合小鼠中出现的发育和生理异常。重点将放在确定cubilin缺乏对HDL代谢的影响。为了在这些研究中使用，我们开发了一种新的cubilin缺乏症小鼠模型。也有一个计划，以开发一个条件敲除模型，以表征cubilin的肾脏特异性功能。第二个目的是确定三种已知的cubilin共受体中的每一种，megalin，megalonless（AMN）和阳离子非依赖性甘露糖6-磷酸/胰岛素样生长因子II-受体（CIMPR），对母体HDL的胚胎摄取过程的意义。这些研究将包括评价HDL的卵黄囊内胚层运输，以确定其是否靶向溶酶体或通过胞吞转运穿过VE。第三个目的是定义配体结合和cubilin的内吞功能的分子基础，主要目的是绘制cubilin内HDL、载脂蛋白A-I和共受体的结合位点。总之，这些研究将为cubilin在母胚脂蛋白转运、胚胎发育和成人肾功能中的功能提供新的见解。

DESCRIPTION (provided by applicant): Cubilin is a peripheral membrane protein that works in conjunction with its co-receptor megalin to mediate endocytosis of high density lipoproteins (HDL) in the yolk sac visceral endoderm (VE) and in renal proximal tubules. The significance of cubilin mediated HDL uptake to embryonic development as well as adult physiology is not known. During development, it is hypothesized that cubilin activity is essential for embryonic acquisition of maternal HDL-associated cholesterol, phospholipids, triglycerides and/or lipid soluble vitamins required to support embryogenesis. The vital role served by yolk sac cubilin is indicated by the severe developmental abnormalities observed when cubilin antibodies are administered to pregnant rats or to embryos cultured ex utero. In adult physiology, it is hypothesized that renal cubilin/megalin uptake of HDL is involved in a feedback mechanism that influences steady state levels of HDL in the blood. Support for this hypothesis comes from our findings that conditional deficiency of renal megalin activity causes an increase in plasma HDL. To test the above hypotheses, and to characterize fundamental mechanistic features of cubilin function, three specific aims are proposed. The first aim is to characterize the developmental and physiological abnormalities that arise in mice homozygous and heterozygous for targeted deletion of the cubilin gene. Emphasis will be placed on determining of the impact of cubilin deficiency on HDL metabolism. For use in these studies we have developed a novel mouse model of cubilin deficiency. There is also a plan to develop a conditional knockout model to characterize the renal-specific functions of cubilin. The second aim is to determine the significance of each of the three known cubilin co-receptors, megalin, amnionless (AMN) and the cation-independent mannose 6-phosphate/insulin-like growth factor ll-receptor (CIMPR), to the process of embryonic uptake of maternal HDL. These studies will include evaluation of yolk sac endodermal trafficking of HDL to determine whether it is targeted to lysosomes or transported across the VE via transcytosis. The third aim is to define the molecular basis for ligand binding and endocytotic functions of cubilin with the primary objectives being to map binding sites within cubilin for HDL, apolipoprotein A-l and the co-receptors. Together, these studies will provide new insights into the function of cubilin in maternal-embryonic.lipoprotein transport, embryonic development and adult kidney function.