Department of Medicine, McGill University Health Center, Montreal, Quebec, Canada.
Institut de Recherches Cliniques de Montréal (IRCM), Department of Medicine (Program of Molecular Biology), Université de Montréal, Montreal, Quebec, Canada; Department of Biochemistry, Université de Montréal, Montreal, Quebec, Canada; Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada.
Kidney Int. 2017 Aug;92(2):349-364. doi: 10.1016/j.kint.2017.03.010. Epub 2017 May 6.
Hyper-activation of Rac1, a small GTPase, in glomerular podocytes has been implicated in the pathogenesis of familial proteinuric kidney diseases. However, the role of Rac1 in acquired nephrotic syndrome is unknown. To gain direct insights into this, we generated a transgenic mouse model expressing a doxycycline-inducible constitutively active form of Rac1 (CA-Rac1) in podocytes. Regardless of the copy number, proteinuria occurred rapidly within five days, and the histology resembled minimal change disease. The degree and severity of proteinuria were dependent on the transgene copy number. Upon doxycycline withdrawal, proteinuria resolved completely (one copy) or nearly completely (two copy). After one month of doxycycline treatment, two-copy mice developed glomerulosclerosis that resembled focal segmental glomerulosclerosis (FSGS) with urinary shedding of transgene-expressing podocytes. p38 MAPK was activated in podocytes upon CA-Rac1 induction while a p38 inhibitor attenuated proteinuria, podocyte loss, and glomerulosclerosis. Mechanistically, activation of Rac1 in cultured mouse podocytes reduced adhesiveness to laminin and induced redistribution of β1 integrin, and both were partially reversed by the p38 inhibitor. Activation of Rac1 in podocytes was also seen in kidney biopsies from patients with minimal change disease and idiopathic FSGS by immunofluorescence while sera from the same patients activated Rac1 in cultured human podocytes. Thus, activation of Rac1 in podocytes causes a spectrum of disease ranging from minimal change disease to FSGS, due to podocyte detachment from the glomerular basement membrane that is partially dependent on p38 MAPK.
Rac1 是一种小 GTPase，其在肾小球足细胞中的过度激活与家族性蛋白尿性肾脏疾病的发病机制有关。然而，Rac1 在获得性肾病综合征中的作用尚不清楚。为了直接了解这一点，我们生成了一种转基因小鼠模型，该模型在足细胞中表达一种可诱导的组成性激活形式的 Rac1（CA-Rac1）。无论拷贝数如何，蛋白尿在五天内迅速发生，组织学表现类似于微小病变性肾病。蛋白尿的程度和严重程度取决于转基因拷贝数。停用强力霉素后，蛋白尿完全（一个拷贝）或几乎完全（两个拷贝）缓解。在强力霉素处理一个月后，两个拷贝的小鼠发生类似于局灶节段性肾小球硬化症（FSGS）的肾小球硬化症，伴有转染表达的足细胞尿脱落。CA-Rac1 诱导后，p38 MAPK 在足细胞中被激活，而 p38 抑制剂可减轻蛋白尿、足细胞丢失和肾小球硬化症。在机制上，在培养的小鼠足细胞中激活 Rac1 会降低其对层粘连蛋白的黏附性并诱导β1 整合素的重新分布，而 p38 抑制剂部分逆转了这两种作用。免疫荧光显示，在微小病变性肾病和特发性 FSGS 的患者肾活检中也可见足细胞中 Rac1 的激活，而来自同一患者的血清可激活培养的人足细胞中的 Rac1。因此，足细胞中 Rac1 的激活可导致从微小病变性肾病到 FSGS 的一系列疾病，这是由于足细胞从肾小球基底膜上脱离，部分依赖于 p38 MAPK。
