Proximal tubule endocytosis in normal and nephrotic kidneys

摘要 连接肾脏近端小管(PT)的细胞的主要功能是恢复逃逸的蛋白质 肾小球滤过屏障，以维持无蛋白质的尿液。PT细胞的顶端内吞作用明显 受流体剪切力(FSS)的变化调节，推测是为了使蛋白质在 肾小球滤过率(GFR)正常变化。大的多配体受体Megalin和 Cubilin/Amnionless(CUBAM)表达于甲状旁腺细胞的根尖表面，并介导甲状旁腺功能亢进。 &gt；50种不同血浆蛋白的内化。尽管PT在回收蛋白质中起着关键作用 从超滤液中，我们对这一段的细胞如何适应的了解令人惊讶地少 不同的过滤负荷，以维持无蛋白尿液。基本问题，包括如何稳健 PT顶端内吞途径的发展和维持，megalin和CUBAM的单独作用 白蛋白摄取中的受体，PT细胞如何对白蛋白浓度或肾小管血流的变化做出反应 速率和内化白蛋白的命运仍然存在争议。我们开发了一种新的细胞培养物 重述体内PT细胞形态和功能特征的模型 和快速调节白蛋白的顶端内吞作用。我们将结合研究使用这些细胞 在小鼠模型中，以解决关于PT细胞如何对正常和 血流和过滤蛋白负荷的病理变化：1)PT细胞如何发展和维持高水平 能力顶端内吞途径？2)Meggalin和CUBAM如何促进白蛋白摄取 正常和肾病状态？3)PT如何在细胞内对GFR的急性变化作出反应？ 4)白蛋白超载时，内吞作用如何影响PT细胞的细胞毒反应？

Abstract A major function of cells linking the proximal tubule (PT) of the kidney is to recover proteins that escape the glomerular filtration barrier to maintain a protein-free urine. Apical endocytosis in PT cells is acutely modulated by changes in fluid shear stress (FSS), presumably to enable efficient protein uptake over normal variations in glomerular filtration rate (GFR). The large multiligand receptors megalin and cubilin/amnionless (CUBAM) are expressed at the apical surface of PT cells and mediate the internalization of >50 different plasma proteins. Despite the critical role of the PT in reclaiming proteins from the ultrafiltrate, we know surprisingly little about how the cells lining this segment accommodate variations in filtered load to maintain a protein free urine. Fundamental issues, including how the robust PT apical endocytic pathway is developed and maintained, the individual role of megalin and CUBAM receptors in albumin uptake, how PT cells respond to changes in albumin concentration or tubular flow rate, and the fate of internalized albumin remain controversial. We have developed a new cell culture model that recapitulates morphological and functional features of PT cells in vivo necessary for efficient and rapidly modulated apical endocytosis of albumin. We will use these cells in conjunction with studies in mouse models to address the following questions about how PT cells respond to normal and pathologic variations in flow and filtered protein load: 1) How do PT cells develop and maintain a high capacity apical endocytic pathway? 2) How do megalin and CUBAM contribute to albumin uptake under normal and nephrotic conditions? 3) How does the PT respond endocytically to acute changes in GFR? and 4) How does endocytosis contribute to cytotoxic responses of PT cells during albumin overload?