Malyankar U M, Almeida M, Johnson R J, Pichler R H, Giachelli C M
Department of Pathology, University of Washington, Seattle, USA.
Kidney Int. 1997 Jun;51(6):1766-73. doi: 10.1038/ki.1997.243.
Osteopontin is a secreted, arginine-glycine-aspartate (RGD)-containing phosphoprotein that is up-regulated in kidney cortical tubular epithelial cells in many experimental models of tubulointerstitial fibrosis. Its close association with infiltrating macrophage in this disease and its ability to directly stimulate macrophage migration has made it a key target as a molecule likely to be important in mediating renal inflammation. The mechanism responsible for osteopontin up-regulation in kidney disease is unknown, but may involve induction by specific cytokines released by damaged glomeruli or other parts of the kidney, prior to the onset of interstitial disease. We have investigated this hypothesis by testing the effects of angiotensin II, bFGF, TGF beta 1, EGF, and IGF, important renal cytokines, on osteopontin regulation in cultured NRK52E cells, a rat renal epithelial cell line. Using Northern blot, Western blot, and ELISA analyses, we find that NRK52E cells constitutively express low levels of osteopontin mRNA and protein. TGF beta 1 and EGF are potent inducers of osteopontin mRNA and protein in those cells. mRNA stability and nuclear run on assays suggest that induction of osteopontin expression by TGF beta 1 and EGF is via increased transcription of the osteopontin gene. In contrast, IGF-1, angiotensin II, and PDGF BB did not significantly modulate osteopontin expression in NRK52E cells. These studies are consistent with the hypothesis that release of potent cytokines by the injured kidney might be one mechanism whereby elevated levels of osteopontin are synthesized by cortical tubular epithelial cells early in tubulointerstitial disease.
骨桥蛋白是一种分泌型的、含精氨酸 - 甘氨酸 - 天冬氨酸（RGD）的磷蛋白，在许多肾小管间质纤维化实验模型中，其在肾皮质肾小管上皮细胞中表达上调。它在这种疾病中与浸润性巨噬细胞密切相关，并且具有直接刺激巨噬细胞迁移的能力，这使其成为一个关键靶点，作为一种可能在介导肾脏炎症中起重要作用的分子。肾病中骨桥蛋白上调的机制尚不清楚，但可能涉及在间质疾病发作之前，由受损肾小球或肾脏其他部位释放的特定细胞因子诱导。我们通过测试血管紧张素 II、碱性成纤维细胞生长因子（bFGF）、转化生长因子β1（TGFβ1）、表皮生长因子（EGF）和胰岛素样生长因子（IGF）（重要的肾脏细胞因子）对培养的NRK52E细胞（一种大鼠肾上皮细胞系）中骨桥蛋白调节的影响，来研究这一假设。使用Northern印迹、Western印迹和酶联免疫吸附测定（ELISA）分析，我们发现NRK52E细胞组成性地表达低水平的骨桥蛋白mRNA和蛋白质。TGFβ1和EGF是这些细胞中骨桥蛋白mRNA和蛋白质的有效诱导剂。mRNA稳定性和细胞核转录活性分析表明，TGFβ1和EGF对骨桥蛋白表达的诱导是通过增加骨桥蛋白基因的转录实现的。相比之下，IGF - 1、血管紧张素II和血小板衍生生长因子BB（PDGF BB）并未显著调节NRK52E细胞中骨桥蛋白的表达。这些研究与以下假设一致，即受损肾脏释放强效细胞因子可能是肾小管间质疾病早期皮质肾小管上皮细胞合成骨桥蛋白水平升高的一种机制。
