The role of cyclin dependent kinase-5 in podocytes differentiation and maintenance of podocytes shape and its function.

本研究利用HIV肾病小鼠模型，探讨细胞周期蛋白依赖性激酶5（CDK 5）在足细胞分化、维持足细胞形态和功能中的作用。利用podocin启动子和tet-on系统，产生主要在足细胞中表达HIV辅助蛋白Vpr之一的小鼠（rtTA-Vpr）。通过半肾切除术和多西环素给药的组合，小鼠发展为塌陷或细胞型局灶性节段性硬化症，伴有大量蛋白尿，类似于人类HIV相关肾病。在肾小球硬化的发展过程中，观察到足细胞的去分化。使用该模型，我们检测了CDK 5的表达。在足细胞脱分化过程中，CDK 5的表达逐渐减少甚至消失。足细胞分化的标志物，如WT-1和synaptopodin，同样减少和消失。我们还研究了细胞周期蛋白D3，它结合CDK 5，但不激活CDK 5。细胞周期蛋白D3的表达也减少或消失。相反，在去分化足细胞中检测到细胞增殖标记物PCNA，表明这些细胞处于增殖的细胞周期中。在光镜下观察到的足细胞形态学上没有变化，但此时已经检测到大量蛋白尿。总之，在HIV肾病小鼠模型中，在足细胞去分化过程中，CDK 5及其相关蛋白减少并消失，其中观察到大量蛋白尿和肾小球硬化。这些结果表明，CDK 5及其相关蛋白在分化的足细胞中发挥作用，以维持其功能。这些分子的丢失可能导致蛋白尿和肾小球硬化。

We investigated the role of cyclin dependent kinase 5 (CDK5) in podocytes differentiation and the maintenance of podocytes shape and its function, using mice model of HIV nephropathy. The mice (rtTA-Vpr) were generated to express one of HIV accessory protein, Vpr, predominantly in podocytes, using podocin promoter and tet-on system. By the combination of heminephrectomy and administration of doxycycline, mice developed collapsing or cellular type focal segmental sclerosis with massive proteinuria, resembling human HIV-associated nephropathy. During the development of glomerulosclerosis, dedifferentiation of podocytes was observed. Using this model, we examined the expression of CDK5. The expression of CDK5 decreased and disappeared during the dedifferentiation of podocytes. The markers of podocytes differentiation, such as WT-1 and synaptopodin, similarly decreased and disappeared. We also examined cyclin D3, which binds to CDK5, but not activates CDK5. The expression of cyclin D3 also decreased and disappeared. On the contrary, PCNA, the marker of cell proliferation was detected in dedifferentiated podocytes, demonstrating that these cells were in cell cycle for proliferation. These changes were observed in the podocytes those did not changed morphologically by a light microscope, although at the time when massive proteinuria was already detected.In conclusion, CDK5 and its related protein were shown to decrease and disappear during the podocytes dedifferentiation in mice model of HIV nephropathy, in which massive proteinuria and glomeruloselerosis were observed. These results suggest that CDK5 and its related protein play a role in differentiated podocytes to maintain its function. Loss of these molecules may lead to proteinuria and glomerulosclerosis.