Abstract
Nuclear factor erythroid 2–related factor 2 (Nrf2) is a transcriptional activator of antioxidant response elements (ARE), which function to increase expression of antioxidant enzymes. Recent works suggests Nrf2 activation is a promising protective mechanism against the progressive neurodegeneration in Parkinson’s disease (PD). While Nrf2 inducers show some promising results in animal models of PD, the response is limit in dopaminergic neurons with the protection mostly conferred by surrounding glia. The present study characterizes ARE transcriptional repressors Bach1 and Bach 2 (Broad complex– Tramtrack–Bric-a-brac and Cap n’ Collar homology, basic leucine zipper transcription factors 1 and 2) as a potential explanation for limited Nrf2 activity in these neurons. The current work identified Bach1 and Bach2 in dopaminergic neurons of the human substantia nigra by immunocytochemical analyses. We further identified Bach2 as a more robust inhibitor of Nrf2 responses. The effects of both Bach1 and Bach2 were dependent on their DNA-binding domains, but the DNA-binding domains did not entirely explain the differences in their relative repressor activities. Using IMR-32 neuroblastoma cells, we found differentiation into a dopaminergic neuronal phenotype resulted in increased Bach2 expression, decreased full-length Bach1 expression, increased truncated Bach1, and blunted Nrf2-mediated responses. Bach inhibitors cobalt protoporphyrin or cadmium chloride, which were more effective against Bach1 than Bach2, did not rescue Nrf2 responses. These results provide a novel mechanism for the lack of antioxidant responses and sensitivity of dopaminergic neurons to oxidative damage, in addition to proposing Bach2 as a novel drug target for the treatment of PD.
Significance Oxidative stress and damage are unifying contributors to explain the progressive loss of dopaminergic neurons in Parkinson’s disease (PD). Although increased transcription of antioxidant enzymes by nuclear factor erythroid 2-related factor 2 (Nrf2) shows potential in combating oxidative damage, Nrf2 protection is mostly conferred by surrounding glia with a relative inability of neurons to mount a protective response. This work characterizes transcriptional repressors Bach1 and Bach2 that inhibit Nrf2 responses and prevent antioxidant enzyme production. This study supports Bach2 as a major factor in preventing antioxidant production in neurons and as a novel drug target to protect against PD.
