Evidence for megalin-mediated proximal tubular uptake of L-FABP, a carrier of potentially nephrotoxic molecules
Evidence for megalin-mediated proximal tubular uptake of L-FABP, a carrier of potentially nephrotoxic molecules
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DOI：
10.1038/labinvest.3700240
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发表时间：
2005-04-01
影响因子：
5
通讯作者：
Saito, A
中科院分区：
文献类型：
--
作者：
Oyama, Y;Takeda, T;Saito, A
肝型脂肪酸结合蛋白（Liver-type fatty acid binding protein，L-FABP）与游离脂肪酸、胆汁酸和胆红素等具有肾毒性的疏水性分子结合，主要在肝细胞中参与其代谢。L-FABP被释放到循环中，肝损伤患者的血浆L-FABP水平升高。L-FABP也存在于肾小管中;然而，L-FABP的精确定位及其在肾小管中的潜在作用尚不清楚。在这项研究中，我们研究了L-FABP在大鼠肾脏的细胞和亚细胞定位，并试图确定L-FABP在肾组织中的起源。肾脏切片的免疫组织化学研究定位于近端小管细胞（PTC）的溶酶体中的L-FABP。在大鼠四氯化碳（CCl 4）诱导的急性肝损伤，我们检测到高水平的L-FABP在循环和肾脏与对照组大鼠相比，通过免疫印迹，而逆转录聚合酶链反应显示，L-FABP mRNA表达水平低，并没有从对照组大鼠的肾脏。当大鼠静脉注射S-35-L-FABP时，肾脏比肝脏和心脏更优先摄取S-35-L-FABP，肾脏切片的组织放射自显影显示S-35-L-FABP通过PTC的顶端结构域内化。石英晶体微天平分析表明，L-FABP绑定到megalin，多配体的内吞受体PTC，在Ca 2+依赖的方式。使用表达megalin的大鼠卵黄囊肿瘤衍生的L2细胞的降解试验表明，megalin介导的细胞摄取和catenorization的I-125-L-FABP。总之，发现循环中的L-FABP被肾小球过滤，并可能通过megalin介导的内吞作用被PTC内化。这些结果表明，一种新的肾脏摄取途径L-FABP，疏水分子的载体，其中一些可能发挥肾毒性作用。
Liver-type fatty acid binding protein (L-FABP) binds with high affinity to hydrophobic molecules including free fatty acid, bile acid and bilirubin, which are potentially nephrotoxic, and is involved in their metabolism mainly in hepatocytes. L-FABP is released into the circulation, and patients with liver damage have an elevated plasma L-FABP level. L-FABP is also present in renal tubules; however, the precise localization of L-FABP and its potential role in the renal tubules are not known. In this study, we examined the cellular and subcellular localization of L-FABP in the rat kidney and tried to determine from where the L-FABP in kidney tissues had originated. Immunohistochemical studies of kidney sections localized L-FABP in the lysosomes of proximal tubule cells (PTC). In rats with carbon tetrachloride (CCl4)-induced acute liver injury, we detected high levels of L-FABP in the circulation and in the kidney compared with those in the control rat by immunoblotting, while reverse transcription-polymerase chain reaction showed that the level of L-FABP mRNA expression in the kidney of CCl4-treated rats was low and did not differ from that in the control rat. When S-35-L-FABP was intravenously administered to rats, the kidneys took up S-35-L-FABP more preferentially than the liver and heart, and histoautoradiography of kidney sections revealed that S-35-L-FABP was internalized via the apical domains of PTC. Quartz-crystal microbalance analysis revealed that L-FABP bound to megalin, a multiligand endocytotic receptor on PTC, in a Ca2+-dependent manner. Degradation assays using megalin-expressing rat yolk sac tumor-derived L2 cells demonstrated that megalin mediated the cellular uptake and catabolism of I-125-L-FABP. In conclusion, circulatory L-FABP was found to be filtered by glomeruli and internalized by PTC probably via megalin-mediated endocytosis. These results suggest a novel renal uptake pathway for L-FABP, a carrier of hydrophobic molecules, some of which may exert nephrotoxic effects.