Saturated fatty acids bound to albumin enhance osteopontin expression and cleavage in renal proximal tubular cells.
Saturated fatty acids bound to albumin enhance osteopontin expression and cleavage in renal proximal tubular cells.
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发表时间：
2018-03
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通讯作者：
Alyssa Cobbs;Kristopher Ballou;Xiaoming Chen;J. George;Xueying Zhao
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作者：
Alyssa Cobbs;Kristopher Ballou;Xiaoming Chen;J. George;Xueying Zhao
骨桥蛋白（OPN）是糖尿病动物和肾病患者肾脏中上调的促炎细胞因子之一。尿白蛋白和白蛋白结合脂肪酸（FA）的增加为蛋白尿肾病（包括糖尿病肾病）的近端小管提供了促炎环境。本研究旨在检测FA超负荷是否能刺激肾小管上皮细胞OPN的表达和裂解。在Zucker糖尿病（ZD）大鼠的肾脏和培养的近端肾小管细胞中检测OPN基因和蛋白表达，所述近端肾小管细胞暴露于牛血清白蛋白（BSA）或与棕榈酸（PA）结合的BSA，最丰富的饱和血浆FA。实时荧光定量PCR分析证实了肾皮质OPN基因的上调与7-20周龄ZD大鼠的蛋白尿和肾病进展相关。肾切片免疫荧光染色显示，在白蛋白超载的ZD大鼠近端小管中大量诱导OPN蛋白。在糖尿病肾脏和尿液样本中进一步证实了完整和切割的OPN蛋白的显著增加，这通过使用血管紧张素II受体阻断剂氯沙坦的抗蛋白尿治疗而减弱。当暴露于不含脂肪酸的BSA时，NRK-52 E细胞表现出全长和切割的OPN蛋白水平的增加。此外，在PA（250-500 µM）存在下，OPN片段的增加大大增强。总之，我们的结果支持白蛋白和结合的FA对肾小管上皮细胞中OPN表达和裂解的刺激作用。因此，除了降低白蛋白尿/蛋白尿之外，减轻循环FA可能是预防和减缓与肥胖和2型糖尿病相关的肾病进展的有效干预。
Osteopontin (OPN) is one of the proinflammatory cytokines upregulated in the kidneys of diabetic animals and patients with nephropathy. An increase in urinary albumin and albumin-bound fatty acids (FA) presents a proinflammatory environment to the proximal tubules in proteinuric kidney diseases including diabetic nephropathy. This study was designed to examine if FA overload could stimulate OPN expression and cleavage in renal tubule epithelial cells. OPN gene and protein expression was examined in the kidney of Zucker diabetic (ZD) rats and cultured proximal tubular cells exposed to either bovine serum albumin (BSA) or BSA conjugated with palmitic acid (PA), the most abundant saturated plasma FA. Real-time PCR analysis confirmed an upregulation of renal cortical OPN gene correlated with albuminuria and nephropathy progression in ZD rats at the age of 7-20 weeks. Immunofluorescence staining of kidney sections revealed a massive induction of OPN protein in albumin-overloaded proximal tubules of ZD rats. A significant increase in both intact and cleaved OPN proteins was further demonstrated in the diabetic kidney and urine samples, which was attenuated by antiproteinuric treatment with losartan, an angiotensin II receptor blocker. When exposed to fatty acid-free BSA, NRK-52E cells exhibited an increase in protein levels of full-length and cleaved OPN. Moreover, the increase in OPN fragments was greatly enhanced in the presence of PA (250-500 µM). Together, our results support a stimulatory effect of albumin and conjugated FA on OPN expression and cleavage in renal tubule epithelial cells. Thus, besides lowering albuminuria/proteinuria, mitigating circulating FAs may be an effective intervention for preventing and slowing down the progression of nephropathy associated with obesity and type 2 diabetes.