Induction of antioxidant and detoxification response by oxidants in cardiomyocytes: Evidence from gene expression profiling and activation of Nrf2 transcription factor

Mild or low doses of oxidants are known to prime cells towards resistance against further damage. In cardiomyocytes, we found that pretreatment with 100 μM H₂O₂ prevents the cells from apoptosis induced by doxorubicin (Dox). Affymetrix microarray analyses of 28,000 genes reveal that H₂O₂ treated cells reduced expression of genes encoding cytochrome c, mitochondrial complex I, III, IV and V and several contractile proteins. Elevated expression of antioxidant and detoxification genes appears as a dominant feature of the gene expression profile of H₂O₂ treated cells. Most of the genes in this category contain an Antioxidant Response Element (ARE) in their promoters. Measurements of ARE promoter-reporter gene activity indicate a dose- and time-dependent activation of the ARE by H₂O₂. Since the Nrf2 transcription factor regulates ARE-mediated gene expression, we overexpressed Nrf2 to test whether activation of Nrf2 is sufficient to induce cytoprotection. High levels of Nrf2 expression were achieved via adenovirus mediated gene delivery. Transduced Nrf2 was present in the nuclei and caused an increase in the expression of NAD(P)H:quinone oxidoreductase 1 (NQO1), a representative downstream target of Nrf2. Unlike H₂O₂ pretreated cells, the cells expressing high levels of Nrf2 were not resistant to Dox-induced apoptosis. Therefore, the cytoprotective effect of H₂O₂ pretreatment is not reliant upon Nrf2 activation alone as measured by resistance against Dox-induced apoptosis.