Frataxin-Deficiency in the Heart Results in an Impaired Nrf2 Response: A Dual Mechanism Mediated via Up-Regulation of Keap1 and GSK3β Axis

Amy Anzovino, Shannon Chiang, Bronwyn E Brown, Clare L Hawkins, Des R Richardson, Michael LH Huang, Free Radical Biology and Medicine, Volume 100, Supplement, November 2016, Pages S143-S144, ISSN 0891-5849, doi:10.1016/j.freeradbiomed.2016.10.376.

Using the MCK conditional frataxin knockout (KO) mouse, which exhibits a cardiomyopathy that mimics the human disease, we examined the Nrf2 antioxidant response pathway in the frataxin-deficient heart. Our studies demonstrated protein and GSH oxidation in the KO relative to wild-type (WT) littermates. Despite this, we found decreased total and nuclear Nrf2 protein levels and increased Keap1-mediated Nrf2 degradation in the heart. Moreover, we also demonstrated the involvement of Gsk3β-dependent export and degradation of nuclear Nrf2 in the heart, as evident by: increased Gsk3β activation; increased Fyn phosphorylation, mediating nuclear export; and increased expression of β-TrCP, a substrate recognition subunit of the E3 ubiqitin ligase complex that is involved in Nrf2 degradation. Furthermore, electrophoretic mobility shift assays demonstrated decreased Nrf2-DNA-binding activity and a general decrease in target gene expression in frataxin KO hearts. These results indicate the blunted anti-oxidant response in the frataxin-deficient heart is, at least in part, due to reduced Nrf2 activity caused by its increased degradation via the Keap1 and Gsk3β pathways.