4-hydroxy-2-nonenal and diethyl-maleate

Sustained activation of the c-Jun NH(2)-terminal kinase (JNK) signaling pathway mediates the development and progression of experimental diet-induced nonalcoholic fatty liver disease (NAFLD). Delineating the mechanism of JNK overactivation in the setting of a fatty liver is therefore essential to understanding the pathophysiology of NAFLD. Both human and experimental NAFLD are associated with oxidative stress and resultant lipid peroxidation, which have been proposed to mediate the progression of this disease from simple steatosis to steatohepatitis. The ability of oxidants and the lipid peroxidation product 4-hydroxynonenal (HNE) to activate JNK signaling suggested that these two factors may act synergistically to trigger JNK overactivation. The effect of HNE on hepatocyte injury and JNK activation was therefore examined in cells under chronic oxidant stress from overexpression of the prooxidant enzyme cytochrome P450 2E1 (CYP2E1), which occurs in NAFLD. CYP2E1-generated oxidant stress sensitized a rat hepatocyte cell line to death from normally nontoxic concentrations of HNE. CYP2E1-overexpressing cells underwent a more profound depletion of glutathione (GSH) in response to HNE secondary to decreased gamma-glutamylcysteine synthetase activity. GSH depletion led to overactivation of JNK/c-Jun signaling at the level of mitogen-activated protein kinase kinase 4 that induced cell death. Oxidant stress and the lipid peroxidation product HNE cause synergistic overactivation of the JNK/c-Jun signaling pathway in hepatocytes, demonstrating that HNE may not be just a passive biomarker of hepatic oxidant stress but rather an active mediator of hepatocellular injury through effects on JNK signaling.

Topics: Aldehydes; Animals; Apoptosis; Catalase; Cell Death; Cell Line, Transformed; Cytochrome P-450 CYP2E1; Extracellular Signal-Regulated MAP Kinases; Glutamate-Cysteine Ligase; Glutathione; Glutathione Transferase; Heat-Shock Response; Hepatocytes; Hydrogen Peroxide; JNK Mitogen-Activated Protein Kinases; Maleates; Malondialdehyde; MAP Kinase Kinase 4; Necrosis; Oxidative Stress; Phosphorylation; Proto-Oncogene Proteins c-jun; Rats; Reactive Oxygen Species; Signal Transduction; Transcription Factor AP-1; Transfection

CD36 is an important scavenger receptor mediating uptake of oxidized low-density lipoproteins (oxLDLs) and plays a key role in foam cell formation and the pathogenesis of atherosclerosis. We report the first evidence that the transcription factor Nrf2 is expressed in vascular smooth muscle cells, and demonstrate that oxLDLs cause nuclear accumulation of Nrf2 in murine macrophages, resulting in the activation of genes encoding CD36 and the stress proteins A170, heme oxygenase-1 (HO-1), and peroxiredoxin I (Prx I). 4-Hydroxy-2-nonenal (HNE), derived from lipid peroxidation, was one of the most effective activators of Nrf2. Using Nrf2-deficient macrophages, we established that Nrf2 partially regulates CD36 expression in response to oxLDLs, HNE, or the electrophilic agent diethylmaleate. In murine aortic smooth muscle cells, expressing negligible levels of CD36, both moderately and highly oxidized LDL caused only limited Nrf2 translocation and negligible increases in A170, HO-1, and Prx I expression. However, treatment of smooth muscle cells with HNE significantly enhanced nuclear accumulation of Nrf2 and increased A170, HO-1, and Prx I protein levels. Because PPAR-gamma can be activated by oxLDLs and controls expression of CD36 in macrophages, our results implicate Nrf2 as a second important transcription factor involved in the induction of the scavenger receptor CD36 and antioxidant stress genes in atherosclerosis.

Topics: Adaptor Proteins, Signal Transducing; Aldehydes; Animals; Aorta; Arteriosclerosis; CD36 Antigens; DNA-Binding Proteins; Female; Gene Expression Regulation; Heat-Shock Proteins; Heme Oxygenase (Decyclizing); Heme Oxygenase-1; Homeodomain Proteins; Lipid Peroxidation; Lipoproteins, LDL; Macrophages, Peritoneal; Maleates; Membrane Proteins; Mice; Mice, Inbred ICR; Mice, Knockout; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; NF-E2-Related Factor 2; Oxidative Stress; Receptors, Cytoplasmic and Nuclear; Receptors, Immunologic; Receptors, Scavenger; Rosiglitazone; Sequestosome-1 Protein; Thiazolidinediones; Trans-Activators; Transcription Factors; Transcription, Genetic; Up-Regulation