Molina-Jijón Eduardo, Rodríguez-Muñoz Rafael, Namorado María del Carmen, Pedraza-Chaverri José, Reyes José L
Department of Physiology, Biophysics, and Neuroscience, Center for Research and Advanced Studies of the National Polytechnic Institute, México, DF 07360, Mexico.
Department of Biology, Faculty of Chemistry, National Autonomous University of Mexico, 04510 University City, DF, Mexico.
Free Radic Biol Med. 2014 Jul;72:162-75. doi: 10.1016/j.freeradbiomed.2014.03.040. Epub 2014 Apr 12.
Renal complications in diabetes are severe and may lead to renal insufficiency. Early alterations in tight junction (TJ) proteins in diabetic nephropathy (DN) have not been explored and the role of oxidative stress in their disassembly has been poorly characterized. We investigated the expression and distribution of TJ proteins: claudin-5 in glomeruli (GL), occludin and claudin-2 in proximal tubules (PTs), and ZO-1 and claudin-1, -4, and -8 in distal tubules (DTs) of rats 21 days after streptozotocin injection. Redox status along the nephron segments was evaluated. Diabetes increased kidney injury molecule-1 expression. Expression of sodium glucose cotransporters (SGLT1 and SGLT2) and facilitative glucose transporter (GLUT2) was induced. Increased oxidative stress was present in GL and PTs and to a lesser extent in DTs (measured by superoxide production and PKCβ2 expression), owing to NADPH oxidase activation and uncoupling of the endothelial nitric oxide synthase-dependent pathway. Claudin-5, occludin, and claudin-2 expression was decreased, whereas claudin-4 and -8 expression increased. ZO-1 was redistributed from membrane to cytosol. Increased nitration of tyrosine residues in claudin-2 was found, which might contribute to decrement of this protein in proximal tubule. In contrast, occludin was not nitrated. We suggest that loss of claudin-2 is associated with increased natriuresis and that loss of glomerular claudin-5 might explain early presence of proteinuria. These findings suggest that oxidative stress is related to alterations in TJ proteins in the kidney that are relevant to the pathogenesis and progression of DN and for altered sodium regulation in diabetes.
糖尿病中的肾脏并发症很严重，可能导致肾功能不全。糖尿病肾病（DN）中紧密连接（TJ）蛋白的早期改变尚未得到研究，氧化应激在其解聚中的作用也未得到充分表征。我们研究了链脲佐菌素注射21天后大鼠肾小球（GL）中claudin-5、近端小管（PTs）中闭合蛋白和claudin-2、远端小管（DTs）中ZO-1以及claudin-1、-4和-8的TJ蛋白表达和分布。评估了沿肾单位各节段的氧化还原状态。糖尿病增加了肾损伤分子-1的表达。诱导了钠葡萄糖共转运蛋白（SGLT1和SGLT2）和易化葡萄糖转运蛋白（GLUT2）的表达。由于NADPH氧化酶激活和内皮型一氧化氮合酶依赖性途径的解偶联，GL和PTs中存在氧化应激增加，DTs中氧化应激增加程度较小（通过超氧化物生成和PKCβ2表达测量）。Claudin-5、闭合蛋白和claudin-2表达降低，而claudin-4和-8表达增加。ZO-1从细胞膜重新分布到细胞质。发现claudin-2中酪氨酸残基的硝化增加，这可能导致该蛋白在近端小管中的减少。相比之下，闭合蛋白未被硝化。我们认为claudin-2的缺失与尿钠排泄增加有关，肾小球claudin-5的缺失可能解释蛋白尿的早期出现。这些发现表明，氧化应激与肾脏中TJ蛋白的改变有关，这些改变与DN的发病机制和进展以及糖尿病中钠调节的改变有关。
