The Effect Of4-hydroxyisoleucine (4-HIL) On Insulin Resistance And Its Molecular Mechanisms In HepG2Cells

AIMS:Insulin resistance is a central pathophysiological feature of atherogenic diseases, includingobesity, dyslipidemia, type2diabetes,coronary artery disease and so on. Previous studieshave indicated that4-hydroxyisoleucine can improve insulin resistance, but the mechanismis unclear. Here, we treated HepG2cells with insulin and high glucose to induce insulinresistance, and wanted to explore the molecular mechanisms of4-hydroxyisoleucineimproving insulin resistance.RESEARCH DESIGH AND METHODS:Insulin-resistant HepG2cells were generated by culturing HepG2cells with insulin andhigh glucose. Glucose oxidase method was used to determine insulin sensitivity. We thentreated insulin-resistance HepG2cells with different concentrations of4-hydroxyisoleucine,and detected the level of TNF-alpha secretion by ELISA assay, the protein expression ofTACE/TIMP3, GLUT4, IRS-1,IRS-2and phosphorylation of IRS-1(Ser307) byWestern-blot.RESULTS:The insulin-induced glucose uptake was reduced in insulin resistant HepG2cells, but couldbe reversed by4-hydroxyisoleucine in a dose dependent manner.4-hydroxyisoleucine hadan impact on TACE/TIMP3system and then reduced the expression of tumor necrosisfactor (TNF)-α. In addition,4-hydroxyisoleucine could regulate the expression of insulin signal transduction proteins(IRS-1/2、GLUT4、phosphorylation of IRS-1)，as shown thatIRS-1and GLUT4were increased, IRS-1phosphorylation (Ser307) was reduced, but hasno impact on IRS-2.CONCLUSIONS:Taken together, these observations suggest that4-hydroxyisoleucine reduced TNF-alphaexpression by adjusting TACE/TIMP3system and then improved insulin resistance, itsmolecular mechanism is to promote the expression of IRS-1and GLUT4, while theregulation of former by lowering the IRS-1serine307phosphorylation levels.