Diabetic nephropathy (DN) is a major microvascular complication of diabetes that can lead to end-stage renal disease. Podocytes constitute the last barrier of glomerular filtration, whose damage are the direct cause of proteinuria. Dopamine receptors are involved in the regulation of diabetes-induced glomerular hyperfiltration, and only dopamine 1 receptor (D1R) can be amplified in cultured mouse podocytes. However, the exact effect of D1R on diabetic podocytes remains unclear. This study aims to investigate the protective role of D1R activation on diabetic podocytes injury in vivo and vitro as well as its potential mechanism. We observed D1R protective effect respectively in streptozotocin (STZ)-induced type 1 diabetes (T1D) mice as well as mouse podocytes (MPC5) cultured in high glucose (HG, 40 mM) medium. It showed that D1R and podocyte-associated proteins (Podocin, CD2AP and Nephrin) expression were significantly decreased both in the T1D mice (fed for 8 and 12 weeks) and HG-cultured MPC5 cells, while the NOX-5 expression increased. In T1D mice, the levels of 24-h urine protein, serum creatinine and urinary 8-OHdG were increased in a time-dependent manner, at the same time, hematoxylin-eosin (HE) staining and electron microscope observed the kidney lesion and podocytes injury. In vitro, HG induced podocytes oxidative stress and apoptosis, which could be inhibited by SKF38393 (a D1R agonist) and N-acetyl-l-cysteine (NAC, a reactive oxygen species scavenger). Furthermore, there was a decreasing Podocin expression and a significant increasing NOX-5 expression in podocytes transfected with D1R-small interfering RNA (siRNA). More importantly, the expression of phospho-CREB (the PKA downstream transcription factor) was decreased and phospho-p38 MAPK was increased in HG-induced podocytes, which can respectively be activated or blocked by SKF38393, 8-Bromo-CAMP (a PKA activator), NAC, and SB20380 (a p38 MAPK inhibitor). In conclusion, D1R activation can protect diabetic podocytes from apoptosis and oxidative damage, in part through the PKA/NOX-5/p38 MAPK pathway.

中文翻译：

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多巴胺1受体激活通过调节PKA / NOX-5 / p38 MAPK轴保护小鼠糖尿病足细胞的损伤。

糖尿病肾病（DN）是糖尿病的主要微血管并发症，可导致终末期肾脏疾病。足细胞构成肾小球滤过的最后障碍，其损害是蛋白尿的直接原因。多巴胺受体参与糖尿病诱导的肾小球超滤的调节，并且仅多巴胺1受体（D1R）可以在培养的小鼠足细胞中扩增。但是，D1R对糖尿病足细胞的确切作用尚不清楚。本研究旨在探讨D1R激活在体内和体外对糖尿病足细胞损伤的保护作用及其潜在机制。我们分别在链脲佐菌素（STZ）诱导的1型糖尿病（T1D）小鼠以及在高葡萄糖（HG，40 mM）培养基中培养的小鼠足细胞（MPC5）中观察到D1R的保护作用。结果表明，T1D小鼠（喂食8周和12周）和HG培养的MPC5细胞中，D1R和足细胞相关蛋白（Podocin，CD2AP和Nephrin）的表达均显着降低，而NOX-5表达升高。在T1D小鼠中，24小时尿蛋白，血清肌酐和尿中的8-OHdG的水平呈时间依赖性增加，同时苏木精-伊红（HE）染色和电子显微镜观察肾病变和足细胞受伤。在体外，HG诱导足细胞氧化应激和凋亡，可被SKF38393（D1R激动剂）和N-乙酰基-1-半胱氨酸（NAC，一种活性氧清除剂）抑制。此外，在用D1R-小干扰RNA（siRNA）转染的足细胞中Podocin表达下降，NOX-5表达显着上升。更重要的是，HG诱导的足细胞中磷酸化CREB（PKA下游转录因子）的表达降低，磷酸化p38 MAPK升高，这可以分别被SKF38393、8-Bromo-CAMP（PKA激活剂），NAC激活或阻断和SB20380（一种p38 MAPK抑制剂）。总之，D1R激活可以部分通过PKA / NOX-5 / p38 MAPK途径保护糖尿病足细胞免于凋亡和氧化损伤。