Ox-PAPC activation of PMET system increases expression of heme oxygenase-1 in human aortic endothelial cell

Abstract

Oxidized-1-palmitoyl-2-arachidonyl-sn -glycerol-3-phosphocholine (Ox-PAPC) has been demonstrated to accumulate in atherosclerotic lesions and regulates expression of more than 1,000 genes in human aortic endothelial cell (HAEC). Among the most highly induced is heme oxygenase-1 (HO-1), a cell-protective antioxidant enzyme, which is sensitively induced by oxidative stress. To identify the pathway by which Ox-PAPC induces HO-1, we focused on the plasma membrane electron transport (PMET) complex, which contains ecto-NADH oxidase 1 (eNOX1) and NADPH:quinone oxidoreductase 1 (NQO1) and affects cellular redox status by regulating levels of NAD(P)H. We demonstrated that Ox-PAPC and its active components stimulated electron transfer through the PMET complex in HAECs from inside to outside [as determined by extracellular 2-(4-iodophenyl)-3-(44-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-1) reduction] and from outside to inside of the cell (as determined by intracellular NBT reduction). Chemical inhibitors of PMET system and siRNAs to PMET components (NQO1 and eNOX1) significantly decreased HO-1 induction by Ox-PAPC. We present evidence that Ox-PAPC activation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in HAEC plays an important role in the induction of HO-1 and PMET inhibitors blocked Nrf2 activation by Ox-PAPC. We hypothesized that PMET activation by Ox-PAPC causes intracellular NAD(P)H depletion, which leads to the increased oxidative stress and HO-1 induction. Supporting this hypothesis, cotreatment of cells with exogenous NAD(P)H and Ox-PAPC significantly decreased oxidative stress and HO-1 induction by Ox-PAPC. Taken together, we demonstrated that the PMET system in HAEC plays an important role in the regulation of cellular redox status and HO-1 expression by Ox-PAPC.

The role of oxidized phospholipids in atherosclerosis

“…Atherogenic pathways upregulated include inflammation, cholesterol synthesis, coagulation, and a decrease in cell division. There was also evidence of oxidative stress responses, including an increase in the anti-atherogenic redox genes and genes associated with the UPR response (12,14,15). Though Ox-PAPC inhibits cells division at 4-6 h after treatment, the same concentration of Ox-PAPC increases angiogenesis seen at 72 h after treatment (16).…”

Nrf2 Signaling, a Mechanism for Cellular Stress Resistance in Long-Lived Mice

“…The expression of at least one PMRS enzyme (NQO1) is under the control of a promoter known as the antioxidant response element (ARE) (54,105). The ARE, also called the EpRE (electrophile response element), is a transcriptional promoter element thought to be important for cellular adaptation to oxidative stress (42,76).…”

Trans-Plasma Membrane Electron Transport in Mammals: Functional Significance in Health and Disease

“…They stated that ENOXs accept reducing equivalents either from membrane-bound hydroquinone or extracellular NADH and that these electrons, depending on the surrounding milieu, can reduce external molecules, such as oxygen, and=or plasma membrane molecules, such as ubiquinone. This hypothesis is corroborated by the observation that extracellular NADH can block cell surface oxygen consumption (109) and can increase reduction of a cell-permeant artificial electron acceptor (166). From these findings, it appears clear that more biochemical studies are needed to fully address the exact functions of ENOX enzymes.…”

“…Conversely, a potential protective role of t-PMET has been reported by Lee and colleagues, who provided evidence that oxidized phospholipids, accumulating in atherosclerotic lesions, activate t-PMET components (NQO1 and ENOX1), which, in turn, lead to NAD(P)H depletion and increased oxidative stress. As a result, the redox-sensitive transcription factor nuclear factor (erythroid-derived 2)-like 2 drives the transcription of heme oxygenase-1 gene, a cell-protective antioxidant enzyme (166).…”