Bach1 differentially regulates distinct Nrf2-dependent genes in human venous and coronary artery endothelial cells adapted to physiological oxygen levels

The effects of physiological oxygen tension on Nuclear Factor-E2-Related Factor 2 (Nrf2)-regulated redox signaling remain poorly understood. We report the first study of Nrf2-regulated signaling in human primary endothelial cells (EC) adapted long-term to physiological O-2 (5%). Adaptation of EC to 5% O-2 had minimal effects on cell ultrastructure, viability, basal redox status or HIF1-alpha expression. Affymetrix array profiling and subsequent qPCR/protein validation revealed that induction of select Nrf2 target genes, HO-1 and NQO1, was significantly attenuated in cells adapted to 5% 02, despite nuclear accumulation and DNA binding of Nrf2. Diminished HO-1 induction under 5% O-2 was stimulus independent and reversible upon re-adaptation to air or silencing of the Nrf2 repressor Bach1, notably elevated under 5% O-2. Induction of GSH-related genes xCT and GCLM were oxygen and Bachl-insensitive during long-term culture under 5% O-2, providing the first evidence that genes related to GSH synthesis mediate protection afforded by Nrf2-Keap1 defense pathway in cells adapted to physiological O-2 levels encountered in vivo. (C) 2015 Elsevier Inc. All rights reserved.