Geniposide accelerates proteasome degradation of Txnip to inhibit insulin secretion in pancreatic β-cells

Purpose To analyze the role of geniposide in the protein degradation of Txnip and to determine the impact of Txnip on geniposide-regulated GSIS in pancreatic INS-1 cells.Methods The content of Txnip protein was measured by western blot; insulin content and glucose uptake were determined by ELISA; and knockdown of Txnip was the method of RNA interference.Results Glucose induces a rapid increase in Txnip protein, and geniposide accelerates the degradation of Txnip via proteasome pathway in the presence of high glucose (25 mM) in INS-1 pancreatic beta-cells. And MG132, a proteasomal inhibitor, potentiates glucose uptake, metabolism (ATP production) and glucose-stimulated insulin secretion (GSIS) in high-glucose (25 mM)-treated INS-1 cells, but geniposide significantly prevents these effects. Furthermore, the combination of geniposide and Txnip knockdown shows substantial synergistic effects to reduce glucose uptake, metabolism and GSIS in high-glucose (25 mM)-treated INS-1 cells.Conclusions Txnip protein played an essential role in glucose uptake, metabolism and GSIS, and geniposide could accelerate the degradation via proteasome pathway in high-glucose-treated pancreatic INS-1 cells.

目的：分析京尼平苷在硫氧还蛋白相互作用蛋白（Txnip）的蛋白质降解中的作用，并确定Txnip对胰腺INS - 1细胞中京尼平苷调节的葡萄糖刺激的胰岛素分泌（GSIS）的影响。方法：采用蛋白质印迹法测定Txnip蛋白含量；采用酶联免疫吸附测定法（ELISA）测定胰岛素含量和葡萄糖摄取量；采用RNA干扰方法敲低Txnip。结果：在INS - 1胰腺β细胞中，葡萄糖诱导Txnip蛋白迅速增加，在高糖（25 mM）存在的情况下，京尼平苷通过蛋白酶体途径加速Txnip的降解。蛋白酶体抑制剂MG132增强高糖（25 mM）处理的INS - 1细胞的葡萄糖摄取、代谢（ATP产生）和葡萄糖刺激的胰岛素分泌（GSIS），但京尼平苷显著抑制这些作用。此外，京尼平苷和Txnip敲低的组合在减少高糖（25 mM）处理的INS - 1细胞的葡萄糖摄取、代谢和GSIS方面显示出显著的协同作用。结论：Txnip蛋白在葡萄糖摄取、代谢和GSIS中起重要作用，京尼平苷可在高糖处理的胰腺INS - 1细胞中通过蛋白酶体途径加速其降解。