Txnip Plays An Essential Role On Geniposide Improving Insulin Resistance In Adipocytes

An impressive number of evidence indicated that thioredoxin interacting protein(Txnip)is a protein kinase mediated by glucose and AMP-dependent protein kinase(AMPK),and plays an essential role on the development and process of with insulin resistance(IR)and type 2 diabetes mellitus(T2DM).Our previous works demonstrated that geniposide could accelerate Txnip degradation to regulate glucose-stimulated insulin secretion in pancreatic beta cells,and decrease blood sugar,improve insulin resistance in db/db mice.At the same time,we also found that geniposide could down-regulate the protein level of Txnip significantly in high glucose-treated adipocytes.But unfortunately,the molecular mechanisms about geniposide accelerating Txnip degradation and its functions need to be explored.Based on the literature and our previous data,we hypothesized that geniposide-mediated Txnip degradation might play an essential role on insulin resistance in adipocytes.Firstly,we probed the effect of geniposide on insulin resistance of adipocytes.The results demonstrated that,in high concentrations of glucose and insulin-induced 3T3-L1 cells,geniposide evidently improve insulin resistance by enhancing the uptake of glucose,up-regulating insulin receptor substrate-1(IRS-1)and glucose transporter 1(GLUT1)and decreasing the phosphorylation of IRS-1 on Ser307 site.Secondly,we design to explore how geniposide decreased the protein level of Txnip in high glucose-treated 3T3-L1 cells.The results from qRT-PCR and western blot indicated that geniposide had no significant influence on the transcription of Txnip,but induced the protein degradation of Txnip through proteasome pathway in 3T3-L1 cells.In order to further clarify the relationship between geniposide promoting Txnip degradation and improving insulin resistance in adipocytes,we knockdown the Txnip expression with siRNA interfere,and then determine measure the effects of geniposide on glucose absorption and insulin signaling factors in adipocytes.The results demonstrated that,in Txnip gene-interfered 3T3-L1 cells,the effect of genipoisde on the uptake of glucose and insulin signaling factors,including IRS-1 and GLUT1 expression,and the phosphorylation of IRS-1 were inhibited significantly.All these data indicated that Txnip might play an critical role in the regulation of glucose uptake and insulin signaling pathway of insulin resistance in adipocytes.And then,the agonist and antagonist for AMPK were collected to investigate thecellular signal transduction pathways of geniposide improving insulin resistance in adipocytes.The results showed that AMPK activators could enhance the effect of geniposide on Txnip degradation and insulin signaling factors,while AMPK antagonists inhibited the effect of geniposide,suggested that AMPK is involved in the effect of geniposide improving insulin resistance in adipocytes.The results of this study indicated that(1)geniposide could improve insulin resistance in adipocytes,(2)geniposide could accelerate the degradation of Txnip in adipocytes through proteasome pathway,(3)Txnip played an essential role on geniposide improving insulin resistance in adipocytes,(4)AMPK was involved in the effect of geniposide on insulin resistance in adipocytes.