Department of Medicine, McGill University Health Centre, Montreal, Que., Canada.
Nephron Exp Nephrol. 2010;114(3):e93-e106. doi: 10.1159/000262317. Epub 2009 Dec 2.
BACKGROUND/AIMS: The function of glomerular podocytes is closely associated with the actin cytoskeleton. In this study, we studied the role of the small Rho-GTPase, Rac1, in actin organization in podocytes.
Conditionally immortalized mouse podocytes (MP) stably expressing nephrin or control plasmid were used.
In MP, Rac1 activity increased significantly at 1 week of differentiation. MP stably expressing nephrin showed Rac1 activity significantly higher and more sustained than vector-expressing control cells. Antibody-mediated cross-linking of nephrin also activated Rac1. Differentiated MP showed more distinct lamellipodia/cellular processes, as compared with undifferentiated cells, which was further augmented by nephrin expression. Transient transfection of constitutively active Rac1 markedly increased the number of lamellipodia/cellular processes in undifferentiated MP, while the Rac1 inhibitor caused actin cytoskeleton derangement in differentiating MP. In the rat model of puromycin aminonucleoside nephrosis, RhoA activity was increased at Day 7 (at the peak of proteinuria), while Rac1 activity increased significantly only at Day 14, when the recovery process had started.
Rac1 is activated in differentiating MP and nephrin potentiates Rac1 activation. Rac1 likely contributes to lamellipodia formation in differentiating MP and may contribute to process formation in podocytes recovering from injuries.
背景/目的：肾小球足细胞的功能与肌动蛋白细胞骨架密切相关。本研究旨在研究小 Rho-GTPase Rac1 在足细胞肌动蛋白组织中的作用。
使用稳定表达nephrin 或对照质粒的条件性永生化小鼠足细胞（MP）。
在分化的第 1 周，MP 中的 Rac1 活性显著增加。稳定表达 nephrin 的 MP 显示 Rac1 活性明显高于和更持久地高于表达载体对照细胞。nephrin 的抗体交联也激活了 Rac1。与未分化的细胞相比，分化的 MP 显示出更明显的片状伪足/细胞突起，而表达 nephrin 则进一步增强了这一作用。瞬时转染组成性激活的 Rac1 显著增加了未分化 MP 中片状伪足/细胞突起的数量，而 Rac1 抑制剂导致分化中的 MP 细胞骨架紊乱。在嘌呤霉素氨基核苷肾病的大鼠模型中，RhoA 活性在第 7 天（蛋白尿高峰期）增加，而 Rac1 活性仅在第 14 天显著增加，此时恢复过程已经开始。
Rac1 在分化的 MP 中被激活，nephrin 增强 Rac1 的激活。Rac1 可能有助于分化中的 MP 中片状伪足的形成，并可能有助于从损伤中恢复的足细胞中过程的形成。
