Sun Ying, Ren Meng, Gao Guan-qi, Gong Bendi, Xin Wei, Guo Hua, Zhang Xiu-juan, Gao Ling, Zhao Jia-jun
Department of Endocrinology, Shandong University, Jinan 250021, China.
Acta Pharmacol Sin. 2008 Apr;29(4):443-50. doi: 10.1111/j.1745-7254.2008.00717.x.
Adenosine monophosphate-activated protein kinase (AMPK), a vital regulator of glucose metabolism, may affect insulin secretion in beta-cells. However, the role of AMPK in beta-cell lipotoxicity remains unclear. Fenofibrate has been reported to regulate lipid homeostasis and is involved in insulin secretion in pancreatic beta-cells. In the present study, we aimed to investigate the effect of palmitate on AMPK expression and glucose-stimulated insulin secretion (GSIS) in rat islets and INS-1 beta-cell, as well as the effect of fenofibrate on AMPK and GSIS in INS-1 cells treated with palmitate.
Isolated rat islets and INS-1 beta-cells were treated with and without palmitate or fenofibrate for 48 h. The mRNA levels of the AMPK alpha isoforms were measured by real-time PCR. Western blotting was used to detect the protein expression of total AMPKalpha (TAMPKalpha), phosphorylated AMPKalpha (P-AMPKalpha), and phosphorylated acetyl coenzyme A carboxylase (P-ACC). Insulin secretion was detected by radioimmunoassay induced by 20 mmol/L glucose as GSIS.
The results showed that chronic exposure of beta-cells to palmitate for 48 h inhibited the expression of AMPK alpha1 mRNA and T-AMPK alpha protein levels, as well as P-AMPK alpha and PACC protein expressions in a dose-dependent manner. Accordingly, GSIS was inhibited by palmitate. Compared with the palmitate-treated cells, fenofibrate ameliorated these changes impaired by palmitate and exhibited a significant elevation in the expression of AMPK alpha and GSIS.
Our findings suggest a role of AMPK alpha reduction in beta-cell lipotoxicity and a novel role of fenofibrate in improving GSIS associated with the AMPK alpha activation in beta-cells chronically exposed to palmitate.
单磷酸腺苷激活的蛋白激酶（AMPK）是葡萄糖代谢的重要调节因子，可能影响β细胞的胰岛素分泌。然而，AMPK在β细胞脂毒性中的作用仍不清楚。据报道，非诺贝特可调节脂质稳态，并参与胰腺β细胞的胰岛素分泌。在本研究中，我们旨在探讨棕榈酸对大鼠胰岛和INS-1β细胞中AMPK表达及葡萄糖刺激的胰岛素分泌（GSIS）的影响，以及非诺贝特对用棕榈酸处理的INS-1细胞中AMPK和GSIS的影响。
将分离的大鼠胰岛和INS-1β细胞分别用或不用棕榈酸或非诺贝特处理48小时。通过实时PCR测定AMPKα亚型的mRNA水平。采用蛋白质印迹法检测总AMPKα（T-AMPKα）、磷酸化AMPKα（P-AMPKα）和磷酸化乙酰辅酶A羧化酶（P-ACC）的蛋白表达。通过放射免疫分析法检测20 mmol/L葡萄糖诱导的胰岛素分泌作为GSIS。
结果显示，β细胞慢性暴露于棕榈酸48小时以剂量依赖的方式抑制了AMPKα1 mRNA的表达、T-AMPKα蛋白水平以及P-AMPKα和P-ACC蛋白表达。相应地，棕榈酸抑制了GSIS。与棕榈酸处理的细胞相比，非诺贝特改善了棕榈酸引起的这些变化，并使AMPKα的表达和GSIS显著升高。
我们的研究结果表明AMPKα减少在β细胞脂毒性中起作用，并且非诺贝特在改善与长期暴露于棕榈酸的β细胞中AMPKα激活相关的GSIS方面具有新作用。
