Inhibiting Bach1 enhanced the activation of Nrf2 signaling and the degradation of HNE in response to oxidative stress.

Abstract

HNE (4-hydroxy-2-nonenal), a primary α, β-unsaturated aldehyde product of lipid peroxidation, is implicated in the pathogenesis and progression of Alzheimer's disease (AD). HNE level in the brain increases with aging and is higher in AD hippocampus than age-matched controls. Upon HNE exposure, cells usually can upregulate HNE detoxification capacity through the activation of Nrf2 signaling. With aging however, the activation of Nrf2 signaling declines. This aging-related decline in Nrf2 signaling would lead to a reduced boost of HNE-detoxification capacity and thus promote HNE accumulation. Prior studies demonstrated that Bach1, a suppressor of Nrf2 signaling, was increased with aging in the brain and involved in the age-related loss of Nrf2 activation. The effect of inhibiting Bach1 on Nrf2 signaling and detoxification of HNE was examined in cultured mouse BV2 microglia. Bach1 was silenced with siRNA or inhibited by 5 uM of hemin or Zinc proporphyrine (ZnPP). The expression of Nrf2 antioxidant genes was measured with qPCR or EpRE/Nrf2 luciferase reporter assay. Binding of Nrf2 or Bach1 to EpRE was determined with chromatin immunoprecipitation (ChIP) assay, and HNE-protein conjugate was determined by Western blot. Knockout or inhibition of Bach1 increased the basal expression of Nrf2-target antioxidant genes (GCLC, GCLM, NQO1, HO-1 and GSTA4-4) and enhanced the induction of these genes by sulforaphane in BV2 microglia. Meanwhile, Bach1 knockout/inhibition significantly increased the degradation of HNE. In addition, inhibition of Bach1 increased the basal and sulforaphane-induced activity of EpRE/Nrf2-luciferase reporter. ChIP assay showed that both Nrf2 and Bach1 bound to the same EpRE (electrophile response element) in the reporter construct. Inhibition of Bach1 enhanced Nrf2 signaling and HNE detoxification. These data suggest that inhibiting Bach1 is a promising approach to prevent age-related decline in Nrf2 signaling and to reduce HNE accumulation-implicated damages.