Farrerol Directly Targets GSK-3β to Activate Nrf2-ARE Pathway and Protect EA.hy926 Cells against Oxidative Stress-Induced Injuries

Oxidative stress-mediated endothelial injury is considered to be involved in the pathogenesis of various cardiovascular diseases. Farrerol, a typical natural flavanone from the medicinal plant Rhododendron dauricum L., has been reported to show protective effects against oxidative stress-induced endothelial injuries in our previous study. However, its action molecular mechanisms and targets are still unclear. In the present study, we determined whether farrerol can interact with glycogen synthase kinase 3β- (GSK-3β-) nuclear factor erythroid 2-related factor 2- (Nrf2-) antioxidant response element (ARE) signaling, which is critical in defense against oxidative stress. Our results demonstrated that farrerol could specifically target Nrf2 negative regulator GSK-3β and inhibit its kinase activity. Mechanistic studies proved that farrerol could induce an inhibitory phosphorylation of GSK-3β at Ser9 without affecting the expression level of total GSK-3β protein and promote the nuclear translocation of Nrf2 as well as the mRNA and protein expression of its downstream target genes heme oxygenase-1 (HO-1) and NAD(P)H: quinone oxidoreductase 1 (NQO1) in EA.hy926 cells. Further studies performed with GSK-3β siRNA and specific inhibitor lithium chloride (LiCl) confirmed that GSK-3β inhibition was involved in farrerol-mediated endothelial protection and Nrf2 signaling activation. Moreover, molecular docking and molecular dynamics studies revealed that farrerol could bind to the ATP pocket of GSK-3β, which is consistent with the ATP-competitive kinetic behavior. Collectively, our results firstly demonstrate that farrerol could attenuate endothelial oxidative stress by specifically targeting GSK-3β and further activating the Nrf2-ARE signaling pathway.