Zhang Xiujuan, Han Wenxia, Jiang Xiuyun, Li Min, Gao Ling, Zhao Jia Jun
Department of Endocrinology, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, Shandong 250021, P.R. China.
The Scientific Center, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, Shandong 250021, P.R. China.
Mol Med Rep. 2014 Jun;9(6):2554-8. doi: 10.3892/mmr.2014.2122. Epub 2014 Apr 8.
Previous studies have demonstrated that sustained high leucine exposure decreases glucose-stimulated insulin secretion (GSIS). However, whether this effect is recoverable following the removal of leucine is unclear. Pancreatic/duodenal homeobox-1 (PDX-1) and its downstream target, glucose transporter 2 (GLUT2), are reported to be positively associated with insulin secretion. However, it also remains unclear whether the effect of leucine on GSIS is accompanied by alterations in PDX-1 and GLUT2. In the present study, insulin secretion, insulin content, PDX-1 and GLUT2 protein expression in INS-1 (rat insulinoma cell line) cells were assessed following a 24-h incubation in 40 mmol/l leucine. Half of the cells were incubated in leucine-free media for a further 24 h to observe the abovementioned effects. In contrast to the control, 40 mmol/l leucine for 24 or 48 h diminished GSIS at high glucose concentrations by 11% (P=0.026) or 22% (P=0.003), insulin content by 14% (P=0.008) or 20% (P=0.002), as well as decreasing PDX-1 and GLUT2 expression. When leucine was removed from the media for a further 24-h incubation, in comparison with those cells that were maintained in leucine treatment for 24 and 48 h, the high GSIS increased by 13% (P=0.032) and 27% (P=0.002), insulin content was augmented by 10% (P=0.014) and 20% (P=0.003), and the protein expression of PDX-1 and GLUT2 also increased. The present study demonstrates that sustained high concentrations of leucine induce a reversible impairment of GSIS and alter insulin content, which is mediated by PDX-1 and GLUT2, in INS-1 cells.
以往的研究表明，持续高剂量亮氨酸暴露会降低葡萄糖刺激的胰岛素分泌（GSIS）。然而，去除亮氨酸后这种效应是否可恢复尚不清楚。据报道，胰腺/十二指肠同源盒-1（PDX-1）及其下游靶点葡萄糖转运蛋白2（GLUT2）与胰岛素分泌呈正相关。然而，亮氨酸对GSIS的影响是否伴随着PDX-1和GLUT2的改变也仍不清楚。在本研究中，将INS-1（大鼠胰岛素瘤细胞系）细胞在40 mmol/L亮氨酸中孵育24小时后，评估其胰岛素分泌、胰岛素含量、PDX-1和GLUT2蛋白表达。将一半细胞在无亮氨酸培养基中再孵育24小时，以观察上述效应。与对照组相比，40 mmol/L亮氨酸处理24或48小时，在高葡萄糖浓度下GSIS分别降低11%（P=0.026）或22%（P=0.003），胰岛素含量分别降低14%（P=0.008）或20%（P=0.002），同时PDX-1和GLUT2表达也降低。当从培养基中去除亮氨酸再孵育24小时时，与持续亮氨酸处理24和48小时的细胞相比，高GSIS分别增加13%（P=0.032）和27%（P=0.002），胰岛素含量分别增加10%（P=0.014）和20%（P=0.003），PDX-1和GLUT2的蛋白表达也增加。本研究表明，持续高浓度亮氨酸会诱导INS-1细胞中GSIS的可逆性损伤并改变胰岛素含量，这是由PDX-1和GLUT2介导的。
