Deletion of nuclear factor-E2-related factor-2 leads to rapid onset and progression of nutritional steatohepatitis in mice
Department of Gastroenterology,Graduate School of Comprehensive Human Sciences, The University of Tsukuba, Tsukuba-shi, Ibaraki, Japan. AJP Gastrointestinal and Liver Physiology
(Impact Factor: 3.8).
11/2009; 298(2):G283-94. DOI: 10.1152/ajpgi.00296.2009
Oxidative stress is a critical mediator in liver injury of steatohepatitis. The transcription factor Nrf2 serves as a cellular stress sensor and is a key regulator for induction of hepatic detoxification and antioxidative stress systems. The involvement of Nrf2 in defense against the development of steatohepatitis remains unknown. We aimed to investigate the protective roles of Nrf2 in nutritional steatohepatitis using wild-type (WT) and Nrf2 gene-null (Nrf2-null) mice. WT and Nrf2-null mice were fed a methionine- and choline-deficient (MCD) diet for 3 and 6 wk, and the liver tissues were analyzed for pathology and for expression levels of detoxifying enzymes and antioxidative stress genes via the Nrf2 transcriptional pathway. In WT mice fed an MCD diet, Nrf2 was potently activated in the livers, and steatohepatitis did not develop over the observation periods. However, in Nrf2-null mice fed an MCD diet, the pathological state of the steatohepatitis was aggravated in terms of fatty changes, inflammation, fibrosis, and iron accumulation. In the livers of the Nrf2-null mice, oxidative stress was significantly increased compared with that of WT mice based on the increased levels of 4-hydroxy-2-nonenal and malondialdehyde. This change was associated with the decreased levels of glutathione, detoxifying enzymes, catalase, and superoxide dismutase activity. Correlating well with the liver pathology, the mRNA levels of factors involved in fatty acid metabolism, inflammatory cytokines, and fibrogenesis-related genes were significantly increased in the livers of the Nrf2-null mice. These findings demonstrate that Nrf2 deletion in mice leads to rapid onset and progression of nutritional steatohepatitis induced by an MCD diet. Activation of Nrf2 could be a promising target toward developing new options for prevention and treatment of steatohepatitis.
Available from: Toshinori Kamisako
- "Nrf2-null mice showed the dysregulation of β-oxidation and the increase in hepatic triglycerides.(18,19) In Nrf2-null mice, the methionine- and choline-deficient diet caused rapid onset and progression of nutritional steatohepatits.(20) Furthermore, Nrf2 activator prevented a high-fat diet induced hepatic lipid accumulation in wild type mice but not in Nrf2-null mice.(21) "
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ABSTRACT: Nuclear factor-E2-related factor 2 (Nrf2) is a regulator of lipid metabolism as well as various cytoprotective enzymes and may be involved in the pathogenesis of non-alcoholic fatty liver disease. Although, bile acids affect lipid metabolism, the role of Nrf2 in bile acid metabolism remains unclear. In this study, it was tested how Nrf2 modulates lipid and bile acid homeostasis in liver in response to changes of cholesterol absorption under high-fat diet using Nrf2-null mice. Eight-week-old male wild-type and Nrf2-null mice (n = 6/group) were divided into three groups fed the following diets: 1) control diet containing 4% soybean oil and 16% lard, 2) control diet plus ezetimibe, 3) control diet plus cholesterol. Blood and livers were removed after 4 weeks feeding. High cholesterol diet increased hepatic expression of liver X receptor α target genes related to fatty acid metabolism (FAS, ACC1, SREBP-1c, SCD-1c and CD36), cholesterol transport (Abcg5/abcg8) and bile acid synthesis (Cyp7a1) in wild type mice. However, these genes were not induced in Nrf2-null mice. These findings suggest that Nrf2 has a relation to liver X receptor α and controls the regulation of gene expressions related to lipid and bile acid metabolism.
Available from: Marthe Ludtmann
- "These findings are consistent with the observed increase in lipid accumulation in the livers of Nrf2-KO mice in comparison with WT (wild-type) animals, most notably in nutritional models of non-alcoholic steatohepatitis [17,18]. Abbreviations: CPT1, carnitine palmitoyltransferase 1; FAO, fatty acid oxidation; FAS, fatty acid synthesis; FCCP, carbonyl cyanide p-trifluoromethoxyphenylhydrazone ; G6PD, glucose-6-phosphate dehydrogenase; HBSS, Hanks balanced salt solution; KD, knockdown; Keap1, Kelch-like ECH-associated protein 1; KO, knockout; LCAD, long-chain acyl-CoA dehydrogenase; MCAD, medium-chain acyl-CoA dehydrogenase; MEF, mouse embryonic fibroblast; NQO1, NAD(P)H:quinone oxidoreductase 1; Nrf2, NF-E2 p45-related factor 2; ROS, reactive oxygen species; SCAD, short-chain acyl-CoA dehydrogenase; TCA, tricarboxylic acid; VLCAD, very-long-chain acyl-CoA dehydrogenase; WT, wild-type Proteomics and immunoblotting analysis have shown that the levels of ATP-citrate lyase, the catalytic action of which provides acetyl-CoA for FAS, are higher in livers of Nrf2-KO mice in comparison with their WT counterparts . Acetyl-CoA serves as a precursor for FAS via its conversion into malonyl-CoA which, in turn, is committed to FAS by its involvement in the elongation of fatty acids through the enzyme activity of fatty acid synthase. "
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ABSTRACT: Transcription factor NF-E2 p45-related factor 2 (Nrf2) regulates the cellular redox homeostasis and cytoprotective responses, allowing adaptation and survival under conditions of stress. The significance of Nrf2 in intermediary metabolism is also beginning to be recognized. Thus, this transcription factor affects negatively fatty acid synthesis. However the effect of Nrf2 on fatty acid oxidation is presently unknown. We now report that the mitochondrial oxidation of long-(palmitic) and short-(hexanoic) chain fatty acids is depressed in the absence of Nrf2 and accelerated when Nrf2 is constitutively active. Addition of fatty acids stimulates respiration in heart and liver mitochondria isolated from wild-type mice. This effect is significantly weaker when Nrf2 is deleted, whereas it is stronger when Nrf2 activity is constitutively high. In the absence of glucose, addition of fatty acids differentially affects the production of ATP in mouse embryonic fibroblasts from wild-type, Nrf2-knockout and Keap1-knockout mice. In acute tissue slices, the rate of regeneration of FADH2 is reduced when Nrf2 is absent. This metabolic role of Nrf2 on fatty acid oxidation has implications for chronic disease conditions including cancer, metabolic syndrome and neurodegeneration.
Available from: PubMed Central
- "Nuclear erythroid 2-related factor 2 (Nrf2) is a significant transcription factor for the induction of a variety of detoxification enzymes, biotransformation enzymes, and xenobiotic efflux transporters, which can regulate up or down inflammatory cytokine genes, fibrogenesis-related genes, and fatty acid metabolism via the Nrf2 transcriptional pathway. It has been proposed that the Nrf2 gene plays a role in NASH because deleting it from mice results in rapid onset and progression of the disease . "
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ABSTRACT: Nonalcoholic fatty liver disease begins with the aberrant accumulation of triglyceride in the liver. Its spectrum includes the earliest stage of hepatic simple steatosis (SS), nonalcoholic steatohepatitis (NASH), cirrhosis, and hepatocellular carcinoma. Generally, hepatic SS is often self-limited; however 10%-30% of patients with hepatic SS progress to NASH. The cause(s) of the transition from SS to NASH are unclear. We aimed to test the contribution of nuclear erythroid 2-related factor 2 (Nrf2) on the progression of "benign" SS to NASH in mice fed a high fat diet. In doing so, we discovered the influence of fatty acid in that progression.
The involvement of Nrf2 in defending against the development of NASH was studied in an experimental model induced by a high-fat diet. Wild-type and Nrf2-null mice were fed the diet. Their specimens were analyzed for pathology as well as for fatty acid content and ratios.Result: In feeding the high-fat diet to the Wild-type and the Nrf2-null mice, the Wild-type mice increased hepatic fat deposition without inflammation or fibrosis (i.e., simple steatosis), while the Nrf2-null mice had significantly more hepatic steatosis and substantial inflammation, (i.e., nonalcoholic steatohepatitis). In addition, as a result of the high-fat diet, SFA (C20: 0, C22: 0) and MUFA (C18: 1, C20: 1) content in Nrf2-null mice were significantly higher than in Wild-type mice. In the Nrf2-null mice the PUFA/TFA ratio decreased; conversely, the MUFA/TFA ratio increased.
The deletion of Nrf2 causes "benign" SS to develop into NASH in mice fed with a high-fat diet, through prompt fatty acid accumulation and disruption of hepatic fatty acid composition in the liver.
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