Anzenberger Uwe, Bit-Avragim Nana, Rohr Stefan, Rudolph Franziska, Dehmel Bastian, Willnow Thomas E, Abdelilah-Seyfried Salim
Max Delbrueck Center (MDC) for Molecular Medicine, Robert-Roessle Str. 10, 13125 Berlin, Germany.
J Cell Sci. 2006 May 15;119(Pt 10):2127-37. doi: 10.1242/jcs.02954. Epub 2006 Apr 25.
Megalin/LRP2 is an endocytic receptor in the proximal tubules of the mammalian kidney that plays a central role in the clearance of metabolites from the glomerular filtrate. To establish a genetic model system for elucidation of molecular components of this retrieval pathway, we characterized orthologous transport processes in the zebrafish. We show that expression of megalin/LRP2 and its co-receptor cubilin is conserved in the larval zebrafish pronephros and demarcates a segment of the pronephric duct that is active in clearance of tracer from the ultrafiltrate. Knock-down of megalin/LRP2 causes lack of Rab4-positive endosomes in the proximal pronephric duct epithelium and abrogates apical endocytosis. Similarly, knock-down of the megalin/LRP2 adaptor Disabled 2 also blocks renal clearance processes. These results demonstrate the conservation of the megalin/LRP2 retrieval pathway between the larval zebrafish pronephros and the mammalian kidney and set the stage for dissection of the renal endocytic machinery in a simple model organism. Using this model system, we provide first genetic evidence that renal tubular endocytosis and formation of endosomes is a ligand-induced process that crucially depends on megalin/LRP2 activity.
巨蛋白/LRP2是哺乳动物肾脏近端小管中的一种内吞受体，在从肾小球滤液中清除代谢产物的过程中起核心作用。为了建立一个用于阐明该回收途径分子成分的遗传模型系统，我们对斑马鱼中的直系同源转运过程进行了表征。我们发现，巨蛋白/LRP2及其共受体 cubilin在斑马鱼幼体前肾中的表达是保守的，并且划定了前肾管中一个对从超滤液中清除示踪剂有活性的节段。敲低巨蛋白/LRP2会导致近端前肾管上皮细胞中缺乏Rab4阳性内体，并消除顶端内吞作用。同样，敲低巨蛋白/LRP2衔接蛋白Disabled 2也会阻断肾脏清除过程。这些结果证明了斑马鱼幼体前肾和哺乳动物肾脏之间巨蛋白/LRP2回收途径的保守性，并为在一个简单的模式生物中剖析肾脏内吞机制奠定了基础。利用这个模型系统，我们提供了首个遗传学证据，即肾小管内吞作用和内体形成是一个配体诱导的过程，该过程关键依赖于巨蛋白/LRP2的活性。
