Role of System LAmino Acid Transporter in Podocyte Cell Biology

我们研究了肾小球中的两种系统L氨基酸转运蛋白LAT2和LAT3。LAT2及其功能配体4F2hc不仅在近端小管中表达，也在足细胞中表达，但其定位在足细胞细胞质中，这表明LAT2在正常成熟足细胞中不具有氨基酸转运蛋白的功能。然而，有趣的是，LAT2在人IgA肾病和anca相关性肾小球肾炎的细胞新月形病变中有高表达。我们利用大鼠月牙状肾小球肾炎模型进一步研究了LAT2在月牙状形成过程中的作用。在月牙形细胞中，mTOR通路下游的S6核糖体蛋白和4E-BP1磷酸化增加，在此之前LAT2和4F2hc表达增加。转染LAT2 cdna的细胞系表现出p70S6K和4E-BP1的主要磷酸化，在LAT功能抑制剂存在时，这种磷酸化明显被消除。综上所述，我们认为LAT2和4F2hc的上调可能参与月牙形成的机制，其机制是生长因子和细胞因子激活的mTOR信号加速了肾小球壁细胞质膜中LAT2和4F2hc的表达，从而通过细胞内支链氨基酸的增加导致mTOR信号的二次诱导。另一方面，LAT3在人和小鼠肾足细胞足突的顶膜中明显表达。培养的小鼠足细胞具有系统L氨基酸转运系统。食物饥饿导致小鼠LAT3蛋白和mRNA表达上调。人类死亡肾显示LAT3开始在s型体肾小球中表达。最后，缺乏LAT3的斑马鱼变形体显示肾小球塌陷，肾小球基底膜增厚，尽管裂隙横膈膜保存完好。我们的数据表明，lat3通过将亮氨酸从鲍曼间隙转运到足细胞细胞质，从而通过哺乳动物靶雷帕霉素-2激活来调节蛋白质合成系统，从而在肾小球发育中起着至关重要的作用。少

We investigated two system L amino acid transporters, LAT2 and LAT3 in the glomerulus. LAT2 and its functional ligand, 4F2hc, was expressed not only in the proximal tubules but also in the podocytes, however, its localization was revealed in the podocyte cytoplasm, suggesting that LAT2 does not function as amino acid transporter in normal mature podocytes. However, interestingly, LAT2 was dearly expressed in the cellular crescent lesion of human IgA nephropathy and ANCA-related glomerulonephritis. We further studied the role of LAT2 in the process of crescent formation by using rat crescent glomerulonephritis model. Increased phosphorylation of S6 ribosomal protein and 4E-BP1, down stream of mTOR pathway, was clearly demonstrated, preceding increase of LAT2 and 4F2hc expression in cellular crescents. LAT2 cDNA-transfected cell line exhibited predominant phosphorylation of p70S6K and 4E-BP1, which was clearly abrogated in the presence of LAT functional inhibitor. Taken together, we conc … More luded that upregulation of LAT2 and 4F2hc could be involved in the crescent formation via the mechanism by which mTOR signaling activated by growth factors and cytokines accelerated LAT2 and 4F2hc expression in the plasma membrane of glomerular parietal cells that leads secondary induction of mTOR signaling through increase of intra cellular branched-chain amino acids. On the other hand, LAT3 was clearly expressed in apical membrane of podocyte foot processes in human and mouse kidney. Cultured mouse podocytes exhibited system L amino acid transport system. Mouse LAT3 protein and mRNA were upregulated by food starvation. The human fatal kidney revealed LAT3 commencing expressing in the S-shaped body glomeruli Finally, zebrafish morphant lacking lat3 revealed collapsed glomerulus with thickened glomerular basement membrane, despite well-preserved slit diaphragm. Dye-injection experiment indicated the disruption of ultrafiltration barrier in zebrafish lat3 morphant Our data suggest that LAT3 plays a crucial role in glomerular development via the mechanism by which LAT3 transports leucine from the Bowman's space to podocyte cytoplasm, leading to the regulation of the protein synthesis system through mammalian target of rapamycin-2 activation. Less