Department of Biology and Biochemistry, University of Houston, Houston, TX, USA.
Department of Biology and Biochemistry, University of Houston, Houston, TX, USA; Department of Medicine, Division of Nephrology, Baylor College of Medicine, Houston, TX, USA.
Biochim Biophys Acta Mol Basis Dis. 2018 Oct;1864(10):3527-3536. doi: 10.1016/j.bbadis.2018.08.007. Epub 2018 Aug 8.
The soluble urokinase receptor (suPAR) has been implicated in the pathogenesis of chronic kidney diseases (CKD) and may function as a circulating "permeability factor" driving primary focal and segmental glomerulosclerosis (FSGS). Here we examined the mechanisms whereby suPAR causes mobilization and increased activation of Ca-permeable TRPC6 channels, which are also implicated in FSGS. Treatment of immortalized mouse podocytes with recombinant suPAR for 24 h caused a marked increase in cytosolic reactive oxygen species (ROS) that required signaling through integrins. This effect was associated with increased assembly of active cell surface NADPH oxidase 2 (Nox2) complexes and was blocked by the Nox2 inhibitor apoycynin. Treatment with suPAR also evoked a functionally measurable increase in TRPC6 channels that was blocked by concurrent treatment with the ROS-quencher TEMPOL as well as by inhibition of Rac1, an essential component of active Nox2 complexes. Elevated ROS evoked by exposing cells to suPAR or HO caused a marked increase in the abundance of tyrosine-phosphorylated proteins including Src, and suPAR-evoked Src activation was blocked by TEMPOL. Moreover, mobilization and increased activation of TRPC6 by suPAR or HO was blocked by concurrent exposure to PP2, an inhibitor of Src family tyrosine kinases. These data suggest that suPAR induces oxidative stress in podocytes that in turn drives signaling through Src family kinases to upregulate TRPC6 channels. The combination of oxidative stress and altered Ca signaling may contribute to loss of podocytes and progression of various forms of CKD.
可溶性尿激酶型纤溶酶原激活物受体（suPAR）与慢性肾脏病（CKD）的发病机制有关，可能作为一种循环的“通透性因子”，驱动原发性局灶节段性肾小球硬化（FSGS）。在这里，我们研究了 suPAR 引起钙通透性 TRPC6 通道动员和激活增加的机制，该通道也与 FSGS 有关。用重组 suPAR 处理永生化的小鼠足细胞 24 小时会导致细胞内活性氧（ROS）明显增加，这需要整合素信号转导。这种效应与活性细胞表面 NADPH 氧化酶 2（Nox2）复合物的组装增加有关，并且可以被 Nox2 抑制剂 apocynin 阻断。用 suPAR 处理还引起可测量的功能性 TRPC6 通道增加，该增加可被 ROS 猝灭剂 TEMPOL 以及 Rac1 抑制剂阻断，Rac1 是活性 Nox2 复合物的必需成分。将细胞暴露于 suPAR 或 H2O2 会引起 ROS 明显增加，导致酪氨酸磷酸化蛋白（包括 Src）的丰度增加，而 suPAR 诱导的 Src 激活可被 TEMPOL 阻断。此外，suPAR 或 H2O2 引起的 TRPC6 的动员和激活增加可被同时暴露于 Src 家族酪氨酸激酶抑制剂 PP2 阻断。这些数据表明，suPAR 在足细胞中诱导氧化应激，进而通过 Src 家族激酶信号转导上调 TRPC6 通道。氧化应激和钙信号改变的组合可能导致足细胞丢失和各种形式的 CKD 进展。
