Lohmann Frithjof, Sachs Marlies, Meyer Tobias N, Sievert Henning, Lindenmeyer Maja T, Wiech Thorsten, Cohen Clemens D, Balabanov Stefan, Stahl R A K, Meyer-Schwesinger Catherine
Department of Internal Medicine, Nephrology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
Department of Internal Medicine, Nephrology, Asklepios Klinikum Barmbek, Hamburg, Germany.
Biochim Biophys Acta. 2014 Jul;1842(7):945-58. doi: 10.1016/j.bbadis.2014.02.011. Epub 2014 Feb 28.
Podocytes are terminally differentiated cells of the glomerular filtration barrier that react with hypertrophy in the course of injury such as in membranous nephropathy (MGN). The neuronal deubiquitinase ubiquitin C-terminal hydrolase L1 (UCH-L1) is expressed and activated in podocytes of human and rodent MGN. UCH-L1 regulates the mono-ubiquitin pool and induces accumulation of poly-ubiquitinated proteins in affected podocytes. Here, we investigated the role of UCH-L1 in podocyte hypertrophy and in the homeostasis of the hypertrophy associated "model protein" p27(Kip1). A better understanding of the basic mechanisms leading to podocyte hypertrophy is crucial for the development of specific therapies in MGN. In human and rat MGN, hypertrophic podocytes exhibited a simultaneous up-regulation of UCH-L1 and of cytoplasmic p27(Kip1) content. Functionally, inhibition of UCH-L1 activity and knockdown or inhibition of UCH-L1 attenuated podocyte hypertrophy by decreasing the total protein content in isolated glomeruli and in cultured podocytes. In contrast, UCH-L1 levels and activity increased podocyte hypertrophy and total protein content in culture, specifically of cytoplasmic p27(Kip1). UCH-L1 enhanced cytoplasmic p27(Kip1) levels by nuclear export and decreased poly-ubiquitination and proteasomal degradation of p27(Kip1). In parallel, UCH-L1 increased podocyte turnover, migration and cytoskeletal rearrangement, which are associated with known oncogenic functions of cytoplasmic p27(Kip1) in cancer. We propose that UCH-L1 induces podocyte hypertrophy in MGN by increasing the total protein content through altered degradation and accumulation of proteins such as p27(Kip1) in the cytoplasm of podocytes. Modification of both UCH-L1 activity and levels could be a new therapeutic avenue to podocyte hypertrophy in MGN.
足细胞是肾小球滤过屏障的终末分化细胞，在诸如膜性肾病（MGN）等损伤过程中会发生肥大反应。神经元去泛素化酶泛素C末端水解酶L1（UCH-L1）在人类和啮齿动物MGN的足细胞中表达并被激活。UCH-L1调节单泛素池，并诱导受影响足细胞中多泛素化蛋白的积累。在此，我们研究了UCH-L1在足细胞肥大以及肥大相关“模型蛋白”p27（Kip1）的稳态中的作用。更好地理解导致足细胞肥大的基本机制对于MGN特异性治疗方法的开发至关重要。在人类和大鼠MGN中，肥大的足细胞同时表现出UCH-L1和细胞质p27（Kip1）含量的上调。在功能上，抑制UCH-L1活性以及敲低或抑制UCH-L1可通过降低分离肾小球和培养足细胞中的总蛋白含量来减轻足细胞肥大。相反，UCH-L1的水平和活性增加了培养物中足细胞的肥大和总蛋白含量，特别是细胞质p27（Kip1）的含量。UCH-L1通过核输出增强细胞质p27（Kip1）水平，并减少p27（Kip1）的多泛素化和蛋白酶体降解。同时，UCH-L1增加了足细胞的更新、迁移和细胞骨架重排，这与细胞质p27（Kip1）在癌症中的已知致癌功能相关。我们提出，UCH-L1通过改变足细胞细胞质中诸如p27（Kip1）等蛋白质的降解和积累来增加总蛋白含量，从而在MGN中诱导足细胞肥大。改变UCH-L1的活性和水平可能是治疗MGN中足细胞肥大的新途径。
