Question: 

The NADPH oxidase isoform NOX4 mainly produces H₂O₂. The transcription factor NRF2 is a key mediator of cellular adaptation to redox stress. Regulation of NOX4 and formation of reactive oxygen species might be directly linked to NO release. Interestingly, NOX4 is the major endothelial NOX isoform and constitutively active. Therefore, regulation of NOX4 on transcriptional level by NRF2 might be directly linked to NO release and endothelial function.

Methods and Results: 

Endothelial cells (HUVEC) were constantly exposed to high laminar shear stress (24h, 30dyn/cm²). This stimulates NO formation and leads to elongation of the cells in the direction of the flow. Previously we could show that NOX4 is the major endothelial NOX isoform and downregulated by shear stress. Here we show that shear stress induces antioxidative response via upregulation of NRF2 which affects NOX4 expression. We transduced HUVEC with lentiviral particles containing short hairpin RNA (sh) against NRF2 and NOX4. Lentiviral downregulation of NOX4 using shNOX4 inhibited the shear stress-dependent elongation of cell shape in response to flow. Furthermore, application of shear stress caused downregulation of NOX4 and upregulation of NRF2 and its target genes NQO-1 and HO-1. Attenuation of NRF2 by shNRF2 inhibited shear stress-dependent induction of NRF2 and its target genes. In addition, shNRF2 enhances the shear stress-dependent downregulation of NOX4. Finally, we could show that downregulation of NOX4 is involved in the upregulation of eNOS in response to flow.

Conclusion: 

Our data suggest a link between NOX4, NRF2-mediated antioxidative response and endothelial function.