Department of Biomedical Sciences, Texas Tech University Health Sciences Center,1300 Coulter Dr., Amarillo, TX 79106, USA.
Am J Physiol Renal Physiol. 2012 Sep;303(5):F766-74. doi: 10.1152/ajprenal.00651.2011. Epub 2012 May 30.
Previously, we have demonstrated human angiotensin type 1 receptor (hAT(1)R) promoter architecture with regard to the effect of high glucose (25 mM)-mediated transcriptional repression in human proximal tubule epithelial cells (hPTEC; Thomas BE, Thekkumkara TJ. Mol Biol Cell 15: 4347-4355, 2004). In the present study, we investigated the role of glucose transporters in high glucose-mediated hAT(1)R repression in primary hPTEC. Cells were exposed to normal glucose (5.5 mM) and high glucose (25 mM), followed by determination of hyperglycemia-mediated changes in receptor expression and glucose transporter activity. Exposure of cells to high glucose resulted in downregulation of ANG II binding (4,034 ± 163.3 to 1,360 ± 154.3 dpm/mg protein) and hAT(1)R mRNA expression (reduced 60.6 ± 4.643%) at 48 h. Under similar conditions, we observed a significant increase in glucose uptake (influx) in cells exposed to hyperglycemia. Our data indicated that the magnitude of glucose influx is concentration and time dependent. In euglycemic cells, inhibiting sodium-glucose cotransporters (SGLTs) with phlorizin and facilitative glucose transporters (GLUTs) with phloretin decreased glucose influx by 28.57 ± 0.9123 and 54.33 ± 1.202%, respectively. However, inhibiting SGLTs in cells under hyperglycemic conditions decreased glucose influx by 53.67 ± 2.906%, while GLUT-mediated glucose uptake remained unaltered (57.67 ± 3.180%). Furthermore, pretreating cells with an SGLT inhibitor reversed high glucose-mediated downregulation of the hAT(1)R, suggesting an involvement of SGLT in high glucose-mediated hAT(1)R repression. Our results suggest that in hPTEC, hyperglycemia-induced hAT(1)R downregulation is largely mediated through SGLT-dependent glucose influx. As ANG II is an important modulator of hPTEC transcellular sodium reabsorption and function, glucose-mediated changes in hAT(1)R gene expression may participate in the pathogenesis of diabetic renal disease.
先前，我们已经研究了人类血管紧张素 I 型受体（hAT（1）R）启动子结构，探讨了高葡萄糖（25mM）介导的人近端肾小管上皮细胞（hPTEC）转录抑制的作用（Thomas BE，Thekkumkara TJ。Mol Biol Cell 15：4347-4355，2004）。在本研究中，我们研究了葡萄糖转运体在高葡萄糖介导的 hAT（1）R 抑制中的作用在原代 hPTEC 中。将细胞暴露于正常葡萄糖（5.5mM）和高葡萄糖（25mM）中，然后测定高血糖介导的受体表达和葡萄糖转运体活性的变化。细胞暴露于高葡萄糖导致 ANG II 结合（4034±163.3 至 1360±154.3dpm/mg 蛋白）和 hAT（1）RmRNA 表达（降低 60.6±4.643%）在 48 小时下降。在类似条件下，我们观察到高糖暴露细胞中葡萄糖摄取（内流）显著增加。我们的数据表明，葡萄糖内流的幅度与浓度和时间呈依赖性。在正常血糖细胞中，用根皮苷抑制钠-葡萄糖协同转运蛋白（SGLTs）和用根皮素抑制易化葡萄糖转运蛋白（GLUTs），可使葡萄糖内流分别减少 28.57±0.9123%和 54.33±1.202%。然而，在高血糖条件下抑制 SGLTs 可使葡萄糖内流减少 53.67±2.906%，而 GLUT 介导的葡萄糖摄取保持不变（57.67±3.180%）。此外，用 SGLT 抑制剂预处理细胞可逆转高葡萄糖介导的 hAT（1）R 下调，表明 SGLT 参与高葡萄糖介导的 hAT（1）R 抑制。我们的结果表明，在 hPTEC 中，高血糖诱导的 hAT（1）R 下调主要通过 SGLT 依赖性葡萄糖内流介导。由于 ANG II 是 hPTEC 细胞间钠离子重吸收和功能的重要调节剂，葡萄糖介导的 hAT（1）R 基因表达变化可能参与糖尿病肾病的发病机制。
