Geniposide improves insulin resistance through AMPK-mediated Txnip protein degradation in 3T3-L1 adipocytes

Thioredoxin-interacting protein (Txnip) has emerged as a key regulator of insulin resistance. In this study, we investigated the roles of geniposide and Txnip in insulin resistance in differentiated 3T3-L1 adipocytes. Our results revealed that geniposide markedly enhanced glucose uptake, increased the protein levels of insulin receptor substrate (IRS)-1 and GLUT-1, and prevented the phosphorylation of IRS-1 and Akt Thr308 induced by insulin resistance in 3T3-L1 adipocytes. We also observed that geniposide accelerated protein degradation of Txnip through proteasome pathway, and knockdown of Txnip with small interfering RNA attenuated the effect of geniposide on insulin signaling molecules, implying that Txnip played a pivotal role in the regulation of insulin signaling molecules by geniposide in 3T3-L1 adipocytes. Furthermore, geniposide induced the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) in the presence of high glucose in differentiated 3T3-L1 adipocytes, while compound C, an inhibitor of AMPK, prevented the effect of geniposide on Txnip degradation and the regulation of glucose uptake and insulin signaling molecules including p-IRS-1, IRS-1, and GLUT-1 in differentiated 3T3-L1 adipocytes. Taken together, all these findings suggest that geniposide improves the insulin signaling defect possibly by AMPK-mediated Txnip degradation in 3T3-L1 adipocytes.