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      Disruption of Nrf2, a Key Inducer of Antioxidant Defenses, Attenuates ApoE-Mediated Atherosclerosis in Mice

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          Abstract

          Background

          Oxidative stress and inflammation are two critical factors that drive the formation of plaques in atherosclerosis. Nrf2 is a redox-sensitive transcription factor that upregulates a battery of antioxidative genes and cytoprotective enzymes that constitute the cellular response to oxidative stress. Our previous studies have shown that disruption of Nrf2 in mice ( Nrf2 −/−) causes increased susceptibility to pulmonary emphysema, asthma and sepsis due to increased oxidative stress and inflammation. Here we have tested the hypothesis that disruption of Nrf2 in mice causes increased atherosclerosis.

          Principal Findings

          To investigate the role of Nrf2 in the development of atherosclerosis, we crossed Nrf2 −/− mice with apoliporotein E-deficient ( ApoE −/−) mice. ApoE −/− and ApoE −/− Nrf2 −/− mice were fed an atherogenic diet for 20 weeks, and plaque area was assessed in the aortas. Surprisingly, ApoE −/− Nrf2 −/− mice exhibited significantly smaller plaque area than ApoE −/− controls (11.5% vs 29.5%). This decrease in plaque area observed in ApoE −/− Nrf2 −/− mice was associated with a significant decrease in uptake of modified low density lipoproteins (AcLDL) by isolated macrophages from ApoE −/− Nrf2 −/− mice. Furthermore, atherosclerotic plaques and isolated macrophages from ApoE −/− Nrf2 −/− mice exhibited decreased expression of the scavenger receptor CD36.

          Conclusions

          Nrf2 is pro-atherogenic in mice, despite its antioxidative function. The net pro-atherogenic effect of Nrf2 may be mediated via positive regulation of CD36. Our data demonstrates that the potential effects of Nrf2-targeted therapies on cardiovascular disease need to be investigated.

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          Most cited references28

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          Disruption of Nrf2 enhances susceptibility to severe airway inflammation and asthma in mice

          Oxidative stress has been postulated to play an important role in the pathogenesis of asthma; although a defect in antioxidant responses has been speculated to exacerbate asthma severity, this has been difficult to demonstrate with certainty. Nuclear erythroid 2 p45-related factor 2 (Nrf2) is a redox-sensitive basic leucine zipper transcription factor that is involved in the transcriptional regulation of many antioxidant genes. We show that disruption of the Nrf2 gene leads to severe allergen-driven airway inflammation and hyperresponsiveness in mice. Enhanced asthmatic response as a result of ovalbumin sensitization and challenge in Nrf2-disrupted mice was associated with more pronounced mucus cell hyperplasia and infiltration of eosinophils into the lungs than seen in wild-type littermates. Nrf2 disruption resulted in an increased expression of the T helper type 2 cytokines interleukin (IL)-4 and IL-13 in bronchoalveolar lavage fluid and in splenocytes after allergen challenge. The enhanced severity of the asthmatic response from disruption of the Nrf2 pathway was a result of a lowered antioxidant status of the lungs caused by lower basal expression, as well as marked attenuation, of the transcriptional induction of multiple antioxidant genes. Our studies suggest that the responsiveness of Nrf2-directed antioxidant pathways may act as a major determinant of susceptibility to allergen-mediated asthma.
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            Role of Nrf2 in the regulation of CD36 and stress protein expression in murine macrophages: activation by oxidatively modified LDL and 4-hydroxynonenal.

            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.
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              Genetic ablation of Nrf2 enhances susceptibility to cigarette smoke-induced emphysema in mice.

              Although inflammation and protease/antiprotease imbalance have been postulated to be critical in cigarette smoke-induced (CS-induced) emphysema, oxidative stress has been suspected to play an important role in chronic obstructive pulmonary diseases. Susceptibility of the lung to oxidative injury, such as that originating from inhalation of CS, depends largely on its upregulation of antioxidant systems. Nuclear factor, erythroid-derived 2, like 2 (Nrf2) is a redox-sensitive basic leucine zipper protein transcription factor that is involved in the regulation of many detoxification and antioxidant genes. Disruption of the Nrf2 gene in mice led to earlier-onset and more extensive CS-induced emphysema than was found in wild-type littermates. Emphysema in Nrf2-deficient mice exposed to CS for 6 months was associated with more pronounced bronchoalveolar inflammation; with enhanced alveolar expression of 8-oxo-7,8-dihydro-2'-deoxyguanosine, a marker of oxidative stress; and with an increased number of apoptotic alveolar septal cells--predominantly endothelial and type II epithelial cells--as compared with wild-type mice. Microarray analysis identified the expression of nearly 50 Nrf2-dependent antioxidant and cytoprotective genes in the lung that may work in concert to counteract CS-induced oxidative stress and inflammation. The responsiveness of the Nrf2 pathway may act as a major determinant of susceptibility to tobacco smoke-induced emphysema by upregulating antioxidant defenses and decreasing lung inflammation and alveolar cell apoptosis.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2008
                21 November 2008
                : 3
                : 11
                : e3791
                Affiliations
                [1 ]Department of Environmental Health Sciences, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, United States of America
                [2 ]Division of Pulmonary and Critical Care Medicine, Department of Medicine, School of Medicine, Johns Hopkins University, Baltimore, Maryland, United States of America
                [3 ]Department of Molecular and Comparative Pathobiology, School of Medicine, Johns Hopkins University, Baltimore, Maryland, United States of America
                Monash University, Australia
                Author notes

                Conceived and designed the experiments: TES JJ KLG VYP SB. Performed the experiments: TES JJ RKT DB MA. Analyzed the data: TES JJ RKT DB. Wrote the paper: TES.

                Article
                08-PONE-RA-05969R1
                10.1371/journal.pone.0003791
                2582492
                19023427
                3e0ed6b6-7f65-4f09-8412-c92372472840
                Sussan et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                History
                : 13 August 2008
                : 4 November 2008
                Page count
                Pages: 9
                Categories
                Research Article
                Genetics and Genomics/Animal Genetics
                Genetics and Genomics/Disease Models
                Cardiovascular Disorders/Vascular Biology

                Uncategorized
                Uncategorized

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