Nrf2 Regulates Antioxidant Gene Expression Evoked by Oxidized Phospholipids in Endothelial Cells and Murine Arteries In Vivo

Abstract

Besides their well-characterized proinflammatory and proatherogenic effects, oxidized phospholipids, such as oxPAPC (oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-phosphocholine) have been shown to have beneficial responses in vascular cells via induction of antioxidant enzymes such as heme oxygenase-1. We therefore hypothesized that oxPAPC could evoke a general cytoprotective response via activation of antioxidative transcription factor Nrf2. Here, we show that oxPAPC increases nuclear accumulation of Nrf2. Using the small interfering RNA approach, we demonstrate that Nrf2 is critical in mediating the induction of glutamate-cysteine ligase modifier subunit (GCLM) and NAD(P)H quinone oxidoreductase-1 (NQO1) by oxPAPC in human endothelial cells, whereas the contribution to the induction of heme oxygenase-1 was less significant. The induction of GCLM and NQO1 was attenuated by reduction of electrophilic groups with sodium borohydrate, as well as treatment with thiol antioxidant N-acetylcysteine, suggesting that the thiol reactivity of oxPAPC is largely mediating its effect on Nrf2-responsive genes. Moreover, we show that oxidized phospholipid having a highly electrophilic isoprostane ring in its sn-2 position is a potent inducer of Nrf2 target genes. Finally, we demonstrate that the oxPAPC-inducible expression of heme oxygenase-1, GCLM, and NQO1 is lower in Nrf2-null than wild-type mouse carotid arteries in vivo. We suggest that the activation of Nrf2 by oxidized phospholipids provides a mechanism by which their deleterious effects are limited in the vasculature.

Reductive metabolism increases the proinflammatory activity of aldehyde phospholipids

“…The nature of this group is also important for the recognition of oxidized phospholipids In endothelial cells, the oxidized phospholipids increase cytokine production and promote monocyte binding. However, consistent with their electrophilic nature, oxidized phospholipids also activate Nrf2-dependent signaling ( 24,25 ) resulting in the increase in phase II detoxifi cation enzymes and protective proteins such as HO-1. They can also prevent the activation of NF-B by TLR4 and thereby prevent lethal endotoxin shock in LPS-injected mice ( 26 ).…”

Nrf2-dependent and -independent Responses to Nitro-fatty Acids in Human Endothelial Cells

“…The residual Nrf2-independent induction of HO-1 may involve a number of potential regulators, as the transcriptional regulation of HO-1 is complex (58). Upon exposure to oxidized phospholipids, both Nrf2 and the cAMP-responsive element-binding protein mediate HO-1 induction in human endothelial cells (25,59). Genome-wide transcriptional profiling of HSF1 target genes using HSF1-null mouse fibroblasts did not show an induction of known ARE target genes (60), further supporting that these two stress responses are distinct and separate.…”

“…Chromatin Immunoprecipitation-Chromatin immunoprecipitation was done as described previously (25). For immunoprecipitation against HSF1, the anti-HSF1 antibody (Cell Signaling) was used.…”

“…2, A and C). To further validate that OA-NO 2 activates ARE-dependent genes, the NQO1 ARE luciferase reporter vector and a vector in which the core ARE was mutated (25) were transfected into HUVECs, and luciferase activity was assessed. OA-NO 2 , but not OA, activated the ARE of the NQO1 gene (supplemental Fig.…”

Inflammation-Related Gene Expression by Lipid Oxidation Derived Products in the Progression of Atherosclerosis

“…Low concentrations of oxPLs do not damage cells, but induce antioxidant enzymes, such as HO-1, known for its anti-inflammatory activity [205]. Induction of HO-1 expression by oxPAPC in HUVECs involves the phosphorylation of CREB, which is also dependent on MAPK pathways [206].…”