NF-E2-related factor 2 inhibits lipid accumulation and oxidative stress in mice fed a high-fat diet

Role of Nrf2 in the pathogenesis of atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the vascular arterial walls. A number of studies have revealed the biological and genetic bases of atherosclerosis, and over 100 genes influence atherosclerosis development. Nrf2 plays an important role in oxidative stress response and drug metabolism, but the Nrf2 signaling pathway is closely associated with atherosclerosis development. During atherosclerosis progression, Nrf2 signaling modulates many physiological and pathophysiological processes, such as lipid homeostasis regulation, foam cell formation, macrophage polarization, redox regulation and inflammation. Interestingly, Nrf2 exhibits both pro- and anti-atherogenic effects in experimental animal models. These observations make the Nrf2 pathway a promising target to prevent atherosclerosis.

Molecular changes associated with chronic liver damage and neoplastic lesions in a murine model of hereditary tyrosinemia type 1

Hereditary tyrosinemia type 1 (HT1) is the most severe inherited metabolic disease of the tyrosine catabolic pathway, with a progressive hepatic and renal injury and a fatal outcome if untreated. Toxic metabolites accumulating in HT1 have been shown to elicit endoplasmic reticulum (ER) stress response, and to induce chromosomal instability, cell cycle arrest and apoptosis perturbation. Although many studies have concentrated on elucidating these events, the molecular pathways responsible for development of hepatocellular carcinoma (HCC) still remain unclear. In this study the fah knockout murine model (fah(-/-)) was used to investigate the cellular signaling implicated in the pathogenesis of HT1. Fah(-/-) mice were subjected to drug therapy discontinuation (Nitisinone withdrawal), and livers were analyzed at different stages of the disease. Monitoring of mice revealed an increasing degeneration of the overall physiological conditions following drug withdrawal. Histological analysis unveiled diffuse hepatocellular damage, steatosis, oval-like cells proliferation and development of liver cell adenomas. Immunoblotting results revealed a progressive and chronic activation of stress pathways related to cell survival and proliferation, including several stress regulators such as Nrf2, eIF2α, CHOP, HO-1, and some members of the MAPK signaling cascade. Impairment of stress defensive mechanisms was also shown by microarray analysis in fah(-/-) mice following prolonged therapy interruption. These results suggest that a sustained activation of stress pathways in the chronic HT1 progression might play a central role in exacerbating liver degeneration.

Concerted action of p62 and Nrf2 protects cells from palmitic acid-induced lipotoxicity

Nonalcoholic fatty liver disease (NAFLD), frequently associated with obesity and diabetes mellitus, is caused by the accumulation of excess fatty acids within liver cells. Palmitic acid (PA), a common saturated fatty acid found in mammals, induces the generation of reactive oxygen species (ROS) and elicits apoptotic cell death, known as lipotoxicity. However, protective mechanisms against PA-induced lipotoxicity have not been elucidated. In this study, we aimed to clarify the role of p62, an adapter protein in the autophagic process, as well as the nuclear factor erythroid 2-related factor 2 (Nrf2)-Kelch-like ECH-associated protein 1 (Keap1) pathway, in protecting cells from PA-induced lipotoxicity. The Nrf2-Keap1 pathway is essential for the protection of cells from oxidative stress. p62 enhances its binding to Keap1 and leads to Nrf2 activation. Here, we show that PA potentiates Keap1 degradation and thereby activates the transcription of Nrf2 target genes partially through autophagy. Furthermore, this PA-mediated Keap1 degradation depends on p62. Correspondingly, a lack of p62 attenuates the PA-mediated Nrf2 activation and increases the susceptibility of cells to oxidative stress. These results indicate that p62 plays an important role in protecting cells against lipotoxicity through Keap1 degradation-mediated Nrf2 activation.

Changing gears in Nrf1 research, from mechanisms of regulation to its role in disease and prevention

The "cap'n'collar" bZIP transcription factor Nrf1 heterodimerizes with small Maf proteins to bind to the Antioxidant Response Element/Electrophile Response Element to transactivate antioxidant enzyme, phase 2 detoxification enzyme and proteasome subunit gene expression. Nrf1 specifically regulates pathways in lipid metabolism, amino acid metabolism, proteasomal degradation, the citric acid cycle, and the mitochondrial respiratory chain. Nrf1 is maintained in the endoplasmic reticulum (ER) in an inactive glycosylated state. Activation involves retrotranslocation from the ER lumen to the cytoplasm, deglycosylation and partial proteolytic processing to generate the active forms of Nrf1. Recent evidence has revealed how this factor is regulated and its involvement in various metabolic diseases. This review outlines Nrf1 structure, function, regulation and its links to insulin resistance, diabetes and inflammation. The glycosylation/deglycosylation of Nrf1 is controlled by glucose levels. Nrf1 glycosylation affects its control of glucose transport, glycolysis, gluconeogenesis and lipid metabolism.

Pregnane X Receptor-Humanized Mice Recapitulate Gender Differences in Ethanol Metabolism but Not Hepatotoxicity

Both human and rodent females are more susceptible to developing alcoholic liver disease following chronic ethanol (EtOH) ingestion. However, little is known about the relative effects of acute EtOH exposure on hepatotoxicity in female versus male mice. The nuclear receptor pregnane X receptor (PXR; NR1I2) is a broad-specificity sensor with species-specific responses to toxic agents. To examine the effects of the human PXR on acute EtOH toxicity, the responses of male and female PXR-humanized (hPXR) transgenic mice administered oral binge EtOH (4.5 g/kg) were analyzed. Basal differences were observed between hPXR males and females in which females expressed higher levels of two principal enzymes responsible for EtOH metabolism, alcohol dehydrogenase 1 and aldehyde dehydrogenase 2, and two key mediators of hepatocyte replication and repair, cyclin D1 and proliferating cell nuclear antigen. EtOH ingestion upregulated hepatic estrogen receptor α, cyclin D1, and CYP2E1 in both genders, but differentially altered lipid and EtOH metabolism. Consistent with higher basal levels of EtOH-metabolizing enzymes, blood EtOH was more rapidly cleared in hPXR females. These factors combined to provide greater protection against EtOH-induced liver injury in female hPXR mice, as revealed by markers for liver damage, lipid peroxidation, and endoplasmic reticulum stress. These results indicate that female hPXR mice are less susceptible to acute binge EtOH-induced hepatotoxicity than their male counterparts, due at least in part to the relative suppression of cellular stress and enhanced expression of enzymes involved in both EtOH metabolism and hepatocyte proliferation and repair in hPXR females.

In vivo delivery of transcription factors with multifunctional oligonucleotides

Therapeutics based on transcription factors have the potential to revolutionize medicine but have had limited clinical success as a consequence of delivery problems. The delivery of transcription factors is challenging because it requires the development of a delivery vehicle that can complex transcription factors, target cells and stimulate endosomal disruption, with minimal toxicity. Here, we present a multifunctional oligonucleotide, termed DARTs (DNA assembled recombinant transcription factors), which can deliver transcription factors with high efficiency in vivo. DARTs are composed of an oligonucleotide that contains a transcription-factor-binding sequence and hydrophobic membrane-disruptive chains that are masked by acid-cleavable galactose residues. DARTs have a unique molecular architecture, which allows them to bind transcription factors, trigger endocytosis in hepatocytes, and stimulate endosomal disruption. The DARTs have enhanced uptake in hepatocytes as a result of their galactose residues and can disrupt endosomes efficiently with minimal toxicity, because unmasking of their hydrophobic domains selectively occurs in the acidic environment of the endosome. We show that DARTs can deliver the transcription factor nuclear erythroid 2-related factor 2 (Nrf2) to the liver, catalyse the transcription of Nrf2 downstream genes, and rescue mice from acetaminophen-induced liver injury.

Bardoxolone Methyl Prevents Fat Deposition and Inflammation in Brown Adipose Tissue and Enhances Sympathetic Activity in Mice Fed a High-Fat Diet

Obesity results in changes in brown adipose tissue (BAT) morphology, leading to fat deposition, inflammation, and alterations in sympathetic nerve activity. Bardoxolone methyl (BARD) has been extensively studied for the treatment of chronic diseases. We present for the first time the effects of oral BARD treatment on BAT morphology and associated changes in the brainstem. Three groups (n = 7) of C57BL/6J mice were fed either a high-fat diet (HFD), a high-fat diet supplemented with BARD (HFD/BARD), or a low-fat diet (LFD) for 21 weeks. BARD was administered daily in drinking water. Interscapular BAT, and ventrolateral medulla (VLM) and dorsal vagal complex (DVC) in the brainstem, were collected for analysis by histology, immunohistochemistry and Western blot. BARD prevented fat deposition in BAT, demonstrated by the decreased accumulation of lipid droplets. When administered BARD, HFD mice had lower numbers of F4/80 and CD11c macrophages in the BAT with an increased proportion of CD206 macrophages, suggesting an anti-inflammatory effect. BARD increased phosphorylation of tyrosine hydroxylase in BAT and VLM. In the VLM, BARD increased energy expenditure proteins, including beta 3-adrenergic receptor (β₃-AR) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). Overall, oral BARD prevented fat deposition and inflammation in BAT, and stimulated sympathetic nerve activity.

The Dual Role of Nrf2 in Nonalcoholic Fatty Liver Disease: Regulation of Antioxidant Defenses and Hepatic Lipid Metabolism

Nonalcoholic fatty liver disease (NAFLD) is a progressive liver disease with ever-growing incidence in the industrialized world. It starts with the simple accumulation of lipids in the hepatocyte and can progress to the more severe nonalcoholic steatohepatitis (NASH), which is associated with inflammation, fibrosis, and cirrhosis. There is increasing awareness that reactive oxygen species and electrophiles are implicated in the pathogenesis of NASH. Transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) is a positive regulator of the expression of a battery of genes involved in the protection against oxidative/electrophilic stress. In rodents, Nrf2 is also known to participate in hepatic fatty acid metabolism, as a negative regulator of genes that promote hepatosteatosis. We review relevant evidence in the literature that these two mechanisms may contribute to the protective role of Nrf2 in the development of hepatic steatosis and in the progression to steatohepatitis, particularly in young animals. We propose that age may be a key to explain contradictory findings in the literature. In summary, Nrf2 mediates the crosstalk between lipid metabolism and antioxidant defense mechanisms in experimental models of NAFLD, and the nutritional or pharmacological induction of Nrf2 represents a promising potential new strategy for its prevention and treatment.

The role of the Nrf2/Keap1 pathway in obesity and metabolic syndrome

Nuclear factor erythroid 2 related factor 2 (Nrf2) is a key regulator of antioxidant signaling that may prevent the development of metabolic syndrome and related cardiovascular diseases. However, emerging evidence shows that lack of Nrf2 could ameliorate insulin resistance, adipogenesis and adipocyte differentiation. Consistent with this, overexpression of Nrf2 gene could also cause insulin resistance under certain conditions. Furthermore, an increasing number of studies indicate that redox balance can be a critical element that contributes to the contradictory effects of Nrf2 on insulin sensitivity and resistance. Reactive oxygen species can promote normal insulin-mediated signal transduction under physiological conditions but also induce insulin resistance under certain pathological conditions. Therefore, the contradictory effects of Nrf2 on insulin signaling pathways may be related to its regulation of redox homeostasis. This review attempts to summarize the latest developments in our understanding of the mechanisms of Nrf2-mediated signaling and its role in the modulation of metabolic homeostasis.

Bovine embryo survival under oxidative-stress conditions is associated with activity of the NRF2-mediated oxidative-stress-response pathway

In present study, we sought to examine the ability of preimplantation bovine embryos to activate the NF-E2-related factor 2 (NRF2)-mediated oxidative-stress response under an oxidative stress environment. In vitro 2-, 4-, 8-, 16-cell-, and blastocyst-stage embryos were cultured under low (5%) or high (20%) oxygen levels. The expression of NRF2, KEAP1 (NRF2 inhibitor), antioxidants downstream of NRF2, and genes associated with embryo metabolism were analyzed between the embryo groups using real-time quantitative PCR. NRF2 and KEAP1 protein abundance, mitochondrial activity, and accumulation of reactive oxygen species (ROS) were also investigated in blastocysts of varying competence that were derived from high- or low-oxygen levels. The expression levels of NRF2 and its downstream antioxidant genes were higher in 8-cell, 16-cell, and blastocyst stages under high oxygen tension, whereas KEAP1 expression was down-regulated under the same conditions. Higher expression of NRF2 and lower ROS levels were detected in early (competent) blastocysts compared to their late (noncompetent) counterparts in both oxygen-tension groups. Similarly, higher levels of active nuclear NRF2 protein were detected in competent blastocysts compared to their noncompetent counterparts. Thus, the survival and developmental competence of embryos cultured under oxidative stress are associated with activity of the NRF2-mediated oxidative stress response pathway during bovine pre-implantation embryo development.

Deficiency in Nrf2 transcription factor decreases adipose tissue mass and hepatic lipid accumulation in leptin-deficient mice

OBJECTIVE

To evaluate whether Nrf2 deficiency impacts insulin resistance and lipid accumulation in liver and white adipose tissue.

METHODS

Lep(ob/ob) mice (OB) with targeted Nrf2 deletion (OB-Nrf2KO) were generated. Pathogenesis of obesity and type 2 diabetes was measured in C57BL/6J, Nrf2KO, OB, and OB-Nrf2KO mice. Hepatic lipid content, lipid clearance, and very low-density lipoprotein (VLDL) secretion were determined between OB and OB-Nrf2KO mice.

RESULTS

OB-Nrf2KO mice exhibited decreased white adipose tissue mass and decreased adipogenic and lipogenic gene expression compared with OB mice. Nrf2 deficiency prolonged hyperglycemia in response to glucose challenge, which was paralleled by reduced insulin-stimulated Akt phosphorylation. In OB mice, Nrf2 deficiency decreased hepatic lipid accumulation, decreased peroxisome proliferator-activated receptor γ expression and nicotinamide adenine dinucleotide phosphate (NADPH) content, and enhanced VLDL secretion. However, this observation was opposite in lean mice. Additionally, OB-Nrf2KO mice exhibited increased plasma triglyceride content, decreased HDL-cholesterol content, and enhanced apolipoprotein B expression, suggesting Nrf2 deficiency caused dyslipidemia in these mice.

CONCLUSIONS

Nrf2 deficiency in Lep(ob/ob) mice reduced white adipose tissue mass and prevented hepatic lipid accumulation but induced insulin resistance and dyslipidemia. This study indicates a dual role of Nrf2 during metabolic dysregulation-increasing lipid accumulation in liver and white adipose tissue but preventing lipid accumulation in obese mice.

Rabbit models for the study of human atherosclerosis: from pathophysiological mechanisms to translational medicine

Laboratory animal models play an important role in the study of human diseases. Using appropriate animals is critical not only for basic research but also for the development of therapeutics and diagnostic tools. Rabbits are widely used for the study of human atherosclerosis. Because rabbits have a unique feature of lipoprotein metabolism (like humans but unlike rodents) and are sensitive to a cholesterol diet, rabbit models have not only provided many insights into the pathogenesis and development of human atherosclerosis but also made a great contribution to translational research. In fact, rabbit was the first animal model used for studying human atherosclerosis, more than a century ago. Currently, three types of rabbit model are commonly used for the study of human atherosclerosis and lipid metabolism: (1) cholesterol-fed rabbits, (2) Watanabe heritable hyperlipidemic rabbits, analogous to human familial hypercholesterolemia due to genetic deficiency of LDL receptors, and (3) genetically modified (transgenic and knock-out) rabbits. Despite their importance, compared with the mouse, the most widely used laboratory animal model nowadays, the use of rabbit models is still limited. In this review, we focus on the features of rabbit lipoprotein metabolism and pathology of atherosclerotic lesions that make it the optimal model for human atherosclerotic disease, especially for the translational medicine. For the sake of clarity, the review is not an attempt to be completely inclusive, but instead attempts to summarize substantial information concisely and provide a guideline for experiments using rabbits.

Protein S exacerbates alcoholic hepatitis by stimulating liver natural killer T cells

BACKGROUND

Alcohol consumption is a major cause of liver injury but the mechanisms are not completely understood. Protein S (PS) is an anticoagulant glycoprotein with multiple functions. The role of PS in liver injury is unknown.

OBJECTIVES

This study investigated the role of PS in acute alcoholic hepatitis.

METHODS

A mouse overexpressing human PS (hPS-TG) was generated in which acute hepatitis was induced by intraperitoneal injection of ethanol.

RESULTS

The levels of serum liver enzymes and liver tissue inflammatory cytokines and the degree of hepatic steatosis were significantly increased in hPS-TG mice treated with ethanol compared with ethanol-treated wild type (WT) mice. Cell expansion, activation and inhibition of apoptosis were significantly augmented in natural killer T (NKT) cells from hPS-TG mice compared with WT mice. Liver mononuclear cells from hPS-TG mice express higher levels of inflammatory cytokines than those from WT mice after stimulation with a specific stimulant of NKT cells in vitro. In a co-culture system of hepatocytes and NKT cells, the effects of PS on ethanol-mediated cell injury were suppressed by a CD1d neutralizing antibody. Alcoholic liver injury was significantly improved in mice pre-treated with PS siRNA and anti-protein S antibody compared with control mice. Patients with alcoholic hepatitis showed significantly increased plasma PS levels and enhanced liver expression of PS and CD1d compared with controls.

CONCLUSIONS

The results of this study suggest that PS exacerbates acute alcoholic hepatitis by inhibiting apoptosis of activated NKT cells.

Liver injury attenuation by curcumin in a rat NASH model: an Nrf2 activation-mediated effect?

AIM

Nuclear factor-erythroid 2-related factor-2 (Nrf2) acts as a defense system in the development of nonalcoholic steatohepatitis (NASH). Curcumin is a phenolic compound with lipid regulatory, anti-oxidative, anti-inflammatory and anti-tumorigenic properties that is beneficial in defending against NASH and was recently proved to be an Nrf2 activator. The aim of this study was to evaluate whether Nrf2 activation could be involved in NASH mitigation by curcumin.

METHODS

Hepatic, metabolic, and inflammatory parameters, along with hepatic Nrf2 protein expression were explored in adult Sprague-Dawley rats developing high-fat-diet-induced NASH and submitted to curcumin gavage for 6 weeks.

RESULTS

Curcumin administration led to lower degrees of hepatic steatosis and inflammation; lower levels of serum aminotransferases, lipids, and homeostasis model assessment of insulin resistance; and lower serum and hepatic contents of tumor necrosis factor-α (TNF-α), interleukin-6, and malondialdehyde. In contrast, higher hepatic contents of glutathione, heme oxygenase-1 and superoxide dismutase were observed in rats with curcumin. Moreover, Nrf2 expression in liver cell nuclei was significantly higher in rats with curcumin.

CONCLUSIONS

Curcumin can prevent and ameliorate NASH via lipid reduction, improve insulin resistance, improve anti-inflammatory, and have antioxidant effects, possibly related to its activation of Nrf2.

Curcumin protects hearts from FFA-induced injury by activating Nrf2 and inactivating NF-κB both in vitro and in vivo

Obesity and increased free fatty acid (FFA) level are tightly linked, leading to the development of cardiovascular disorders. Curcumin is a natural product from Curcuma longa with multiple bioactivities and is known to have cardioprotective effects in several cellular and animal models. The current study was designed to evaluate the cardioprotective effects of curcumin and demonstrate the underlying mechanism in FFA-induced cardiac injury. Using cell culture studies and high fat in vivo model, we explored the mechanistic basis of anti-inflammatory and antioxidant activities of curcumin. We observed that palmitate (PA) treatment in cardiac derived H9C2 cells induced a marked increase in reactive oxygen species, inflammation, apoptosis and hypertrophy. All of these changes were effectively suppressed by curcumin treatment. In addition, oral administration of curcumin at 50mg/kg completely suppressed high fat diet-induced oxidative stress, inflammation, apoptosis, fibrosis, hypertrophy and tissue remodeling in mice. The beneficial actions of curcumin are closely associated with its ability to increase Nrf2 expression and inhibit NF-κB activation. Thus, both in vitro and in vivo studies showed a promising role of curcumin as a cardioprotective agent against palmitate and high fat diet mediated cardiac dysfunction. We indicated the regulatory roles of Nrf2 and NF-κB in obesity-induced heart injury, and suggested that they may be important therapeutic targets in the treatment of obesity-related disorders.

Activation of the Nrf2-ARE pathway in hepatocytes protects against steatosis in nutritionally induced non-alcoholic steatohepatitis in mice

Oxidative stress is implicated in the development of non-alcoholic steatohepatitis (NASH). The Nrf2-antioxidant response element pathway protects cells from oxidative stress. Studies have shown that global Nrf2 deficiency hastens the progression of NASH. The purpose of this study was to determine whether long-term hepatocyte-specific activation of Nrf2 mitigates NASH progression. Transgenic mice expressing a constitutively active Nrf2 construct in hepatocytes (AlbCre+/caNrf2+) and littermate controls were generated. These mice were fed standard or methionine-choline-deficient (MCD) diet, a diet used to induce NASH development in rodents. After 28 days of MCD dietary feeding, mice developed significant increases in steatosis, inflammation, oxidative stress, and HSC activation compared with those mice on standard diet. AlbCre+/caNrf2+ animals had significantly decreased serum transaminases and reduced steatosis when compared with the AlbCre+/caNrf2- animals. This significant reduction in steatosis was associated with increased expression of genes involved in triglyceride export (MTTP) and β-oxidation (CPT2). However, there were no differences in the increased oxidative stress, inflammation, and HSC activation from MCD diet administration between the AlbCre+/caNrf2- and AlbCre+/caNrf2+ animals. We conclude that hepatocyte-specific activation of Nrf2-mediated gene expression decreased hepatocellular damage and steatosis in a dietary model of NASH. However, hepatocyte-specific induction of Nrf2-mediated gene expression alone is insufficient to mitigate inflammation, oxidative stress, and HSC activation in this nutritional NASH model.

Role of Nrf2 in chronic liver disease

Nuclear erythroid 2-related factor 2 (Nrf2) is a central regulator of antioxidative response elements-mediated gene expression. It has a significant role in adaptive responses to oxidative stress by interacting with the antioxidant response element, which induces the expression of a variety of downstream targets aimed at cytoprotection. Previous studies suggested oxidative stress and associated damage could represent a common link between different forms of diseases. Oxidative stress has been implicated in various liver diseases, including viral hepatitis, nonalcoholic fatty liver disease/steatohepatitis, alcoholic liver disease and drug-induced liver injury. Nrf2 activation is initiated by oxidative or electrophilic stress, and aids in the detoxification and elimination of potentially harmful exogenous chemicals and their metabolites. The expression of Nrf2 has been observed throughout human tissue, with high expression in detoxification organs, especially the liver. Thus, Nrf2 may serve as a major regulator of several cellular defense associated pathways by which hepatic cells combat oxidative stress. We review the relevant literature concerning the crucial role of Nrf2 and its signaling pathways against oxidative stress to protect hepatic cell from oxidative damage during development of common chronic liver diseases. We also review the use of Nrf2 as a therapeutic target to prevent and treat liver diseases.

γδ T cells as a major source of IL-17 production during age-dependent RPE degeneration

PURPOSE

Chronic inflammation is a key factor contributing to the progression of age-related macular degeneration (AMD). The goals of the current study were to develop an improved mouse model with retinal pathologic features similar to those of AMD and to characterize the immunoreactive cells in the outer retina and choroid during degeneration of the retinal pigment epithelium (RPE).

METHODS

Mice deficient in nuclear erythroid 2-related factor 2 (Nrf2) at 12 months of age were fed a high-fat, cholesterol-rich diet for up to 16 weeks. Ocular phenotype was monitored by optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) in live animals, and was further validated by retinal histopathology. Immunofluorescence staining of either cryosections or RPE flat mounts was used to define immunoreactive cells. Flow cytometry analyses were further performed to define the subsets of intraocular T lymphocytes.

RESULTS

After 16 weeks on a high-fat (HF) diet, 58% of the eyes from Nrf2-/- mice had progression of retinal lesions. Major histocompatibility complex class II (MHC II)-positive microglia, FoxP3+ regulatory T cells (Tregs), and CD3+ IL-17-producing T cells were detected in either the retina or sub-RPE space. Flow cytometry analyses further revealed that most of the IL-17-producing cells were CD3+ CD4- TCRγδ+ cells.

CONCLUSIONS

The results suggest that the T cell-mediated immune responses played important roles in controlling the progression of AMD-like phenotype in Nrf2-deficient mice.

Protective role of macrophage migration inhibitory factor in nonalcoholic steatohepatitis

MIF is an inflammatory cytokine but is hepatoprotective in models of hepatotoxin-induced liver fibrosis. Hepatic fibrosis can also develop from metabolic liver disease, such as nonalcoholic fatty liver disease (NASH). We investigated the role of MIF in high-fat or methionine- and choline-deficient diet mouse models of NASH. Mif(-/-) mice showed elevated liver triglyceride levels (WT, 53±14 mg/g liver; Mif(-/-), 103±7 mg/g liver; P<0.05) and a 2-3-fold increased expression of lipogenic genes. Increased fatty degeneration in the livers of Mif(-/-) mice was associated with increased hepatic inflammatory cells (1.6-fold increase in F4/80(+) macrophages) and proinflammatory cytokines (e.g., 2.3-fold increase in Tnf-α and 2-fold increase in Il-6 expression). However, inflammatory cells and cytokines were decreased by 50-90% in white adipose tissue (WAT) of Mif(-/-) mice. Subset analysis showed that macrophage phenotypes in livers of Mif(-/-) mice were skewed toward M2 (e.g., 1.7-fold and 2.5-fold increase in Arg1 and Il-13, respectively, and 2.5-fold decrease in iNos), whereas macrophages were generally reduced in WAT of these mice (70% reduction in mRNA expression of F4/80(+) macrophages). The protective MIF effect was scrutinized in isolated hepatocytes. MIF reversed inflammation-induced triglyceride accumulation in Hepa1-6 cells and primary hepatocytes and also attenuated oleic acid-elicited triglyceride increase in 3T3-L1 adipocytes. Protection from fatty hepatocyte degeneration was paralleled by a 2- to 3-fold reduction by MIF of hepatocyte proinflammatory cytokine production. Blockade of MIF receptor cluster of differentiation 74 (CD74) but not of CXCR2 or CXCR4 fully reverted the protective effect of MIF, comparable to AMPK inhibition. In summary, we demonstrate that MIF mediates hepatoprotection through the CD74/AMPK pathway in hepatocytes in metabolic models of liver injury.

Susceptibility of Nrf2-null mice to steatohepatitis and cirrhosis upon consumption of a high-fat diet is associated with oxidative stress, perturbation of the unfolded protein response, and disturbance in the expression of metabolic enzymes but not with insulin resistance

Mice lacking the transcription factor NF-E2 p45-related factor 2 (Nrf2) develop more severe nonalcoholic steatohepatitis (NASH), with cirrhosis, than wild-type (Nrf2^+/+) mice when fed a high-fat (HF) diet for 24 weeks. Although NASH is usually associated with insulin resistance, HF-fed Nrf2^−/− mice exhibited better insulin sensitivity than HF-fed Nrf2^+/+ mice. In livers of HF-fed mice, loss of Nrf2 resulted in greater induction of lipogenic genes, lower expression of β-oxidation genes, greater reduction in AMP-activated protein kinase (AMPK) levels, and diminished acetyl coenzyme A (CoA) carboxylase phosphorylation than in the wild-type livers, which is consistent with greater fatty acid (FA) synthesis in Nrf2^−/− livers. Moreover, primary Nrf2^−/− hepatocytes displayed lower glucose and FA oxidation than Nrf2^+/+ hepatocytes, with FA oxidation partially rescued by treatment with AMPK activators. The unfolded protein response (UPR) was perturbed in control regular-chow (RC)-fed Nrf2^−/− mouse livers, and this was associated with constitutive activation of NF-κB and JNK, along with upregulation of inflammatory genes. The HF diet elicited an antioxidant response in Nrf2^+/+ livers, and as this was compromised in Nrf2^−/− livers, they suffered oxidative stress. Therefore, Nrf2 protects against NASH by suppressing lipogenesis, supporting mitochondrial function, increasing the threshold for the UPR and inflammation, and enabling adaptation to HF-diet-induced oxidative stress.

Identification and quantification of the basal and inducible Nrf2-dependent proteomes in mouse liver: biochemical, pharmacological and toxicological implications

The transcription factor Nrf2 is a master regulator of cellular defence: Nrf2 null mice (Nrf2^(−/−)) are highly susceptible to chemically induced toxicities. We report a comparative iTRAQ-based study in Nrf2^(−/−) mice treated with a potent inducer, methyl-2-cyano-3,12-dioxooleana-1,9(11)dien-28-oate (CDDO-me; bardoxolone -methyl), to define both the Nrf2-dependent basal and inducible hepatoproteomes. One thousand five hundred twenty-one proteins were fully quantified (FDR < 1%). One hundred sixty-one were significantly different (P < 0.05) between WT and Nrf2^(−/−) mice, confirming extensive constitutive regulation by Nrf2. Treatment with CDDO-me (3 mg/kg; i.p.) resulted in significantly altered expression of 43 proteins at 24 h in WT animals. Six proteins were regulated at both basal and inducible levels exhibiting the largest dynamic range of Nrf2 regulation: cytochrome P4502A5 (CYP2A5; 17.2-fold), glutathione-S-transferase-Mu 3 (GSTM3; 6.4-fold), glutathione-S-transferase Mu 1 (GSTM1; 5.9-fold), ectonucleoside-triphosphate diphosphohydrolase (ENTPD5; 4.6-fold), UDP-glucose-6-dehydrogenase (UDPGDH; 4.1-fold) and epoxide hydrolase (EPHX1; 3.0-fold). These proteins, or their products, thus provide a potential source of biomarkers for Nrf2 activity. ENTPD5 is of interest due to its emerging role in AKT signalling and, to our knowledge, this protein has not been previously shown to be Nrf2-dependent. Only two proteins altered by CDDO-me in WT animals were similarly affected in Nrf2^(−/−) mice, demonstrating the high degree of selectivity of CDDO-me for the Nrf2:Keap1 signalling pathway.

Biological significance

The Nrf2:Keap1 signalling pathway is attracting considerable interest as a therapeutic target for different disease conditions. For example, CDDO-me (bardoxolone methyl) was investigated in clinical trials for the treatment of acute kidney disease, and dimethyl fumarate, recently approved for reducing relapse rate in multiple sclerosis, is a potent Nrf2 inducer. Such compounds have been suggested to act through multiple mechanisms; therefore, it is important to define the selectivity of Nrf2 inducers to assess the potential for off-target effects that may lead to adverse drug reactions, and to provide biomarkers with which to assess therapeutic efficacy. Whilst there is considerable information on the global action of such inducers at the mRNA level, this is the first study to catalogue the hepatic protein expression profile following acute exposure to CDDO-me in mice. At a dose shown to evoke maximal Nrf2 induction in the liver, CDDO-me appeared highly selective for known Nrf2-regulated proteins. Using the transgenic Nrf2^(−/−) mouse model, it could be shown that 97% of proteins induced in wild type mice were associated with a functioning Nrf2 signalling pathway. This analysis allowed us to identify a panel of proteins that were regulated both basally and following Nrf2 induction. Identification of these proteins, which display a large magnitude of variation in their expression, provides a rich source of potential biomarkers for Nrf2 activity for use in experimental animals, and which may be translatable to man to define individual susceptibility to chemical stress, including that associated with drugs, and also to monitor the pharmacological response to Nrf2 inducers.

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Liver proteomes from WT, Nrf2-null and Nrf2-induced mice were compared by iTRAQ

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Of 1521 proteins quantified, 161 were regulated basally and 43 following induction

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Six proteins were both basally and inducibly regulated, with high dynamic ranges

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In order of fold change, these proteins were CYP2A5, GSTM3, GSTM1, ENTPD5, G6PD, EPHX1

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These proteins may yield translatable biomarkers for clinical development

NFE2L2 polymorphisms, mortality, and metabolism in the general population

The nuclear factor (erythroid-derived 2)-like 2 (NFE2L2 or NRF2) gene regulates transcription of enzymes involved in cellular detoxification and lipids homeostasis. NFE2L2 is associated with pathophysiology of atherosclerosis and chronic obstructive pulmonary disease (COPD). Therefore we studied the relation between NFE2L2 and all-cause, cardiovascular, and COPD mortality and its associations with triglyceride and cholesterol levels. We genotyped five tagging single nucleotide polymorphisms (SNPs) (rs4243387, rs2364723, rs13001694, rs1806649, and rs6726395) in NFE2L2 in 1,390 subjects from the Vlagtwedde-Vlaardingen cohort. Participants were examined in 1989/1990 and followed up till the vital status evaluation on December 31st, 2008. Associations between SNPs and mortality were estimated by Cox proportional hazards regression, and associations between SNPs and triglyceride and cholesterol levels were tested with linear regression. After 18 yr, 284 (20.4%) subjects had died, 107 from cardiovascular disease and 20 from COPD. Minor allele carriers of rs13001694 had a significantly reduced risk of all-cause mortality compared with wild types: hazard ratio (HR) 0.8 [95% confidence interval (CI) 0.6 to 1.0]. Minor allele carriers of rs2364723 had significantly reduced risk of cardiovascular mortality: HR = 0.5 (95% CI: 0.3–0.7). This result was consistent in stratified analyses: females 0.4 (0.2–0.7), males 0.6 (0.3–0.9), never smokers 0.5 (0.2–1.1), ever smokers 0.5 (0.3–0.8). Minor allele carriers of rs1806649 had a markedly reduced COPD mortality: HR = 0.3 (95% CI: 0.1–0.9). Rs2364723 was associated with lower triglyceride levels. None of the SNPs was associated with cholesterol levels. This study shows for the first time that NFE2L2 is associated with reduced risk of all-cause, cardiovascular and COPD mortality in humans.

c9,t11-Conjugated linoleic acid ameliorates steatosis by modulating mitochondrial uncoupling and Nrf2 pathway

Oxidative stress, hepatic steatosis, and mitochondrial dysfunction are key pathophysiological features of nonalcoholic fatty liver disease. A conjugated linoleic acid (CLA) mixture of cis9,trans11 (9,11-CLA) and trans10,cis12 (10,12-CLA) isomers enhanced the antioxidant/detoxifying mechanism via the activation of nuclear factor E2-related factor-2 (Nrf2) and improved mitochondrial function, but less is known about the actions of specific isomers. The differential ability of individual CLA isomers to modulate these pathways was explored in Wistar rats fed for 4 weeks with a lard-based high-fat diet (L) or with control diet (CD), and, within each dietary treatment, two subgroups were daily administered with 9,11-CLA or 10,12-CLA (30 mg/day). The 9,11-CLA, but not 10,12-CLA, supplementation to CD rats improves the GSH/GSSG ratio in the liver, mitochondrial functions, and Nrf2 activity. Histological examination reveals a reduction of steatosis in L-fed rats supplemented with both CLA isomers, but 9,11-CLA downregulated plasma concentrations of proinflammatory markers, mitochondrial dysfunction, and oxidative stress markers in liver more efficiently than in 10,12-CLA treatment. The present study demonstrates the higher protective effect of 9,11-CLA against diet-induced pro-oxidant and proinflammatory signs and suggests that these effects are determined, at least in part, by its ability to activate the Nrf2 pathway and to improve the mitochondrial functioning and biogenesis.

Role of Nrf2 in the alteration of cholesterol and bile acid metabolism-related gene expression by dietary cholesterol in high fat-fed mice

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.

Role of pregnane X receptor in obesity and glucose homeostasis in male mice

Clinical obesity is a complex metabolic disorder affecting one in three adults. Recent reports suggest that pregnane X receptor (PXR), a xenobiotic nuclear receptor important for defense against toxic agents and for eliminating drugs and other xenobiotics, may be involved in obesity. Noting differences in ligand specificities between human and mouse PXRs, the role of PXR in high fat diet (HFD)-induced obesity was examined using male PXR-humanized (hPXR) transgenic and PXR-knock-out (PXR-KO) mice in comparison to wild-type (WT) mice. After 16 weeks on either a control diet or HFD, WT mice showed greater weight gain, whereas PXR-KO mice gained less weight due to their resistance to HFD-induced decreases in adipose tissue peroxisome proliferator-activated receptor α and induction of hepatic carnitine palmitoyltransferase 1, suggesting increased energy metabolism. Interestingly, control-fed PXR-KO mice exhibited hepatomegaly, hyperinsulinemia, and hyperleptinemia but hypoadiponectinemia and lower adiponectin receptor R2 mRNA levels relative to WT mice. Evaluation of these biologic indicators in hPXR mice fed a control diet or HFD revealed further differences between the mouse and human receptors. Importantly, although HFD-fed hPXR mice were resistant to HFD-induced obesity, both PXR-KO and hPXR mice exhibited impaired induction of glucokinase involved in glucose utilization and displayed elevated fasting glucose levels and severely impaired glucose tolerance. Moreover, the basal hepatic levels of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase 1 were increased in hPXR mice compared with WT mice. Altogether, although the mouse PXR promotes HFD-induced obesity, the hPXR mouse carries a genetic predisposition for type 2 diabetes and thus provides a model for exploring the role of human PXR in the metabolic syndrome.

Antioxidant effects of fucoxanthin rich powder in rats fed with high fat diet

The purpose of this study was to determine the antioxidant effect of fucoxanthin. After rats were fed a normal fat diet (NF), high fat diet (HF), and high fat with 0.2% fucoxanthin diet (HF + Fxn) for 4 weeks, the markers of oxidative stress and antioxidant capacity like lipid peroxidation, plasma total antioxidant capacity (TAC), and activities of antioxidant enzymes (catalase, superoxide dismutase (SOD), and gluthathione peroxidase (GSH-Px)) were determined. mRNA expression of transcription factor, nuclear erythroid factor like 2 (Nrf2), and its target genes such as NAD(P)H quinone oxidoreductase1 (NQO1) and heme oxygenase-1 (HO-1) were also determined. Mean weight gain in the HF + Fxn group was lower, without statistical significance, and the total food intake in the HF + Fxn group was lower than that in the HF group (P < 0.05). The activity of GSH-Px (P < 0.05) in plasma was significantly higher in the HF + Fxn group than those in the HF group (P < 0.05). In the liver, the activities of catalase (P < 0.05) and GSH-Px (P < 0.05) in the HF + Fxn group were significantly higher than those in the HF group. Plasma TAC level was significantly higher in the HF + Fxn group than that in the HF group (P < 0.05). Lipid peroxidation in plasma tended to be lower without statistical significance. Fucoxanthin supplements were shown to have higher mRNA expression of Nrf2 and NQO1 than those in the high fat diet only group (P < 0.05). In conclusion, supplementation of fucoxanthin improved the antioxidant capacity, depleted by high fat diet, by activating the Nrf2 pathway and its downstream target gene NQO1. Therefore, supplementation of fucoxanthin, especially for those who consume high fat in their diet, may benefit from reduced risk of oxidative stress.

Nrf2 deletion causes "benign" simple steatosis to develop into nonalcoholic steatohepatitis in mice fed a high-fat diet

Background

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.

Method

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.

Conclusion

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.

Keap1-knockdown decreases fasting-induced fatty liver via altered lipid metabolism and decreased fatty acid mobilization from adipose tissue

AIMS

The purpose of this study was to determine whether Nrf2 activation, via Keap1-knockdown (Keap1-KD), regulates lipid metabolism and mobilization induced by food deprivation (e.g. fasting).

METHODS AND RESULTS

Male C57BL/6 (WT) and Keap1-KD mice were either fed ad libitum or food deprived for 24 hours. After fasting, WT mice exhibited a marked increase in hepatic lipid accumulation, but Keap1-KD mice had an attenuated increase of lipid accumulation, along with reduced expression of lipogenic genes (acetyl-coA carboxylase, stearoyl-CoA desaturase-1, and fatty acid synthase) and reduced expression of genes related to fatty acid transport, such as fatty acid translocase/CD36 (CD36) and Fatty acid transport protein (FATP) 2, which may attribute to the reduced induction of Peroxisome proliferator-activated receptor (Ppar) α signaling in the liver. Additionally, enhanced Nrf2 activity by Keap1-KD increased AMP-activated protein kinase (AMPK) phosphorylation in liver. In white adipose tissue, enhanced Nrf2 activity did not change the lipolysis rate by fasting, but reduced expression of fatty acid transporters--CD36 and FATP1, via a PPARα-dependent mechanism, which impaired fatty acid transport from white adipose tissue to periphery circulation system, and resulted in increased white adipose tissue fatty acid content. Moreover, enhanced Nrf2 activity increased glucose tolerance and Akt phosphorylation levels upon insulin administration, suggesting Nrf2 signaling pathway plays a key role in regulating insulin signaling and enhanced insulin sensitivity in skeletal muscle.

CONCLUSION

Enhanced Nrf2 activity via Keap1-KD decreased fasting-induced steatosis, pointing to an important function of Nrf2 on lipid metabolism under the condition of nutrient deprivation.

Caloric restriction-mediated induction of lipid metabolism gene expression in liver is enhanced by Keap1-knockdown

PURPOSE

CR increases fatty acid oxidation to decrease tissue lipid content. The Nuclear factor E2-related factor 2 (Nrf2)-Kelch like ECH associated Protein 1 (Keap1) pathway is an antioxidant gene regulatory pathway that has been previously investigated in weight gain. However, limited interaction of Nrf2/Keap1 and CR exists. The purpose of this study was to determine how Keap1 knockdown (Keap1-KD), which is known to increase Nrf2 activity, affects the CR response, such as weight loss, hepatic lipid decrease, and induction of fatty acid oxidation gene expression.

METHODS

C57BL/6 and Keap1-KD mice were maintained on 40% CR or fed ad libitum for 6 weeks. Hepatic lipid content, lipid metabolic gene, and miRNA expression was quantified.

RESULTS

CR lowered hepatic lipid content, and induced fatty acid oxidation gene expression to a greater degree in Keap1-KD compared to C57BL/6 mice. CR differentially altered miRNA 34a, 370, let-7b* in livers of Keap1-KD compared to C57BL/6 mice.

CONCLUSIONS

CR induced induction of fatty acid oxidation gene expression was augmented with Keap1 knockdown, which was associated with differential expression of several miRNAs implicated in fatty acid oxidation and lipid accumulation.

Glucose availability is a decisive factor for Nrf2-mediated gene expression

Activation of the transcription factor Nrf2 (nuclear factor-erythroid 2-related factor 2) is one of the major cellular defense lines against oxidative and xenobiotic stress, but also influences genes involved in lipid and glucose metabolism. It is unresolved whether the cytoprotective and metabolic responses mediated by Nrf2 are connected or separable events in non-malignant cells. In this study we show that activation of Nrf2, either by the small molecule sulforaphane or knockout of the Nrf2 inhibitor Keap1, leads to increased cellular glucose uptake and increased glucose addiction in fibroblasts. Upon Nrf2 activation glucose is preferentially metabolized through the pentose phosphate pathway with increased production of NADPH. Interference with the supply of glucose or the pentose phosphate pathway and NADPH generation not only hampers Nrf2-mediated detoxification of reactive oxygen species on the enzyme level but also Nrf2-initiated expression of antioxidant defense proteins, such as glutathione reductase and heme-oxygenase1. We conclude that the Nrf2-dependent protection against oxidative stress relies on an intact pentose phosphate pathway and that there is crosstalk between metabolism and detoxification already at the level of gene expression in mammalian cells.

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Activation of Nrf2 results in increased cellular glucose uptake.

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Upon activation of Nrf2 glucose is preferentially metabolized through the PPP.

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The resulting increase in NADPH is not only pivotal for functional detoxification of ROS, but also for Nrf2-dependent gene expression in mammalian cells.

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These data complement our understanding of the metabolic shade of Nrf2 action.

Role of the Nrf2-ARE pathway in liver diseases

The liver is a central organ that performs a wide range of functions such as detoxification and metabolic homeostasis. Since it is a metabolically active organ, liver is particularly susceptible to oxidative stress. It is well documented that liver diseases including hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma are highly associated with antioxidant capacity. NF-E2-related factor-2 (Nrf2) is an essential transcription factor that regulates an array of detoxifying and antioxidant defense genes expression in the liver. It is activated in response to electrophiles and induces its target genes by binding to the antioxidant response element (ARE). Therefore, the roles of the Nrf2-ARE pathway in liver diseases have been extensively investigated. Studies from several animal models suggest that the Nrf2-ARE pathway collectively exhibits diverse biological functions against viral hepatitis, alcoholic and nonalcoholic liver disease, fibrosis, and cancer via target gene expression. In this review, we will discuss the role of the Nrf2-ARE pathway in liver pathophysiology and the potential application of Nrf2 as a therapeutic target to prevent and treat liver diseases.

Deletion of Nrf2 leads to rapid progression of steatohepatitis in mice fed atherogenic plus high-fat diet

BACKGROUND

The transcription factor nuclear factor-E2-related factor-2 (Nrf2) inhibits lipid accumulation and oxidative stress in the liver by interfering with lipogenic pathways and inducing antioxidative stress genes.

METHODS

The involvement of Nrf2 in defense against the development of steatohepatitis was studied in an experimental model induced by an atherogenic plus high-fat (Ath + HF) diet. Wild-type (WT) and Nrf2-null mice were fed the diet. Their specimens were analyzed for pathology as well as for the expression levels of genes involved in fatty acid metabolism and those involved via the Nrf2 transcriptional pathway.

RESULTS

In Nrf2-null mice fed the diet, steatohepatitis developed rapidly, leading to precirrhosis. The Ath + HF diet increased hepatic triglyceride levels and changed fatty acid composition in both mouse groups. However, oleic acid (C18:1 n-9) predominated in the livers of Nrf2-null mice. Correlating well with the pathology, the mRNA levels of the factors involved in fatty acid metabolism (Lxr, Srebp-1a, 1c, Acc-1, Fas, Scd-1, and Fatty acid transporting peptides 1, 3, 4), the inflammatory cytokine genes (Tnf-α and IL-1β), and the fibrogenesis-related genes (Tgf-β1 and α-Sma) were significantly increased in the livers of Nrf2-null mice fed the diet, compared with the levels of these factors in matched WT mice. Oxidative stress was significantly increased in the livers of Nrf2-null mice fed the diet. This change was closely associated with the decreased levels of antioxidative stress genes.

CONCLUSIONS

Nrf2 deletion leads to the rapid onset and progression of steatohepatitis induced by an Ath + HF diet, through both up-regulation of co-regulators of fatty acid metabolism and down-regulation of oxidative metabolism regulators in the liver.

Hepatic gene expression profiling in Nrf2 knockout mice after long-term high-fat diet-induced obesity

Introduction. The transcription factor NFE2-related factor 2 (Nrf2) is a central regulator of antioxidant and detoxification gene expression in response to electrophilic or oxidative stress. Nrf2 has recently been shown to cross-talk with metabolic pathways, and its gene deletion protected mice from high-fat-diet-(HFD-) induced obesity and insulin resistance. This study aimed to identify potential Nrf2-regulated genes of metabolic interest by comparing gene expression profiles of livers of wild-type (WT) versus Nrf2 knockout (Nrf2-KO) mice after a long-term HFD. Methods. WT and Nrf2-KO mice were fed an HFD for 180 days; total RNA was prepared from liver and used for microarray analysis and quantitative real-time RT-PCR (qRT-PCR). Results. The microarray analysis identified 601 genes that were differentially expressed between WT and Nrf2-KO mice after long-term HFD. Selected genes, including ones known to be involved in metabolic regulation, were prioritized for verification by qRT-PCR: Cyp7a1 and Fabp5 were significantly overexpressed in Nrf2-KO mice; in contrast, Car, Cyp2b10, Lipocalin 13, Aquaporin 8, Cbr3, Me1, and Nqo1 were significantly underexpressed in Nrf2-KO mice. Conclusion. Transcriptome profiling after HFD-induced obesity confirms that Nrf2 is implicated in liver metabolic gene networks. The specific genes identified here may provide insights into Nrf2-dependent mechanisms of metabolic regulation.

Bardoxolone methyl analogs RTA 405 and dh404 are well tolerated and exhibit efficacy in rodent models of Type 2 diabetes and obesity

Bardoxolone methyl and related triterpenoids are well tolerated and efficacious in numerous animal models potentially relevant to patients with Type 2 diabetes and chronic kidney disease. These agents enhance glucose control and regulate lipid accumulation in rodent models of diabetes and obesity, and improve renal function, reduce inflammation, and prevent structural injury in models of renal disease. However, a recent study in Zucker diabetic fatty (ZDF) rats noted poor tolerability with the bardoxolone methyl analog RTA 405 within 1 mo after treatment initiation, although this study was confounded in part by the use of an impure RTA 405 batch. To investigate these discordant observations, the present studies were conducted to further characterize triterpenoids in rodent models of diabetes and obesity. A follow-up study was conducted in ZDF rats with two related triterpenoids (RTA 405 and dh404) for 1.5 mo. Consistent with previous rodent experience, and in contrast to the more recent ZDF report, ZDF rats administered RTA 405 or dh404 exhibited no adverse clinical signs, had laboratory values similar to controls, and exhibited no evidence of adverse liver or kidney histopathology. Additionally, RTA 405 was well tolerated in streptozotocin-induced Type 1 diabetic rats and high-fat-diet-induced obese mice. The present results are consistent with the overall published body of data obtained with triterpenoids and provide further evidence that these molecules are well tolerated without adverse effects on hepatobiliary or renal function in rodent models of diabetes and obesity.

Genetic activation of Nrf2 protects against fasting-induced oxidative stress in livers of mice

Acute fasting causes elevated oxidative stress. The current study investigated the effects of the nuclear factor erythoid 2-related factor 2 (Nrf2), the sensor of oxidative stress in cells, on energy homeostasis and liver pathophysiology during fasting. Feed was removed from mice possessing none (Nrf2-null), normal (wild-type, WT), enhanced (Keap1-knockdown, K1-KD), and maximum (hepatocyte-specific Keap1-knockout, K1-HKO) Nrf2 activity in liver for 24 h. Body weight, blood glucose, and blood lipid profiles were similar among mice with graded Nrf2 activity under either fed or fasted conditions. Fasting reduced liver size in mice expressing Nrf2, but not in Nrf2-null mice. Nrf2-null mice accumulated more non-esterified free fatty acids and triglycerides in liver after fasting than the other genotypes of mice. Fatty acids are mainly catabolized in mitochondria, and Nrf2-null mice had lower mitochondrial content in liver under control feeding conditions, which was further reduced by fasting. In contrast, mitochondrial contents in mice with enhanced Nrf2 activity were not affected by fasting. Oxidative stress, determined by staining of free radicals and quantification of malondialdehyde equivalents, was highest in Nrf2-null and lowest in K1-HKO mice after fasting. The exacerbated oxidative stress in livers of Nrf2-null mice is predicted to lead to damages to mitochondria, and therefore diminished oxidation and increased accumulation of lipids in livers of Nrf2-null mice. In summary, the Nrf2-regulated signaling pathway is critical in protecting mitochondria from oxidative stress during feed deprivation, which ensures efficient utilization of fatty acids in livers of mice.

New player on an old field; the keap1/Nrf2 pathway as a target for treatment of type 2 diabetes and metabolic syndrome

Nuclear erythroid factor 2 like 2 (Nrf2) has been described as a transcription factor that serves as a master regulator of the adaptive response to exogenous and endogenous oxidative and electrophilic stresses. Evidence of Nrf2 crosstalk with other molecular pathways is increasing; recent publications have proposed a role of Nrf2 in the development of obesity and in the highly regulated process of adipocyte differentiation through its interaction with other transcription factors and receptors implicated in metabolic regulation. In the present review, we discuss the available data on the possible role of Nrf2 in obesity and metabolic syndrome and the feasibility of using Nrf2 as a therapeutic target in the clinical setting.

Pregnancy represses induction of efflux transporters in livers of type I diabetic mice

PURPOSE

To determine whether down-regulation of transcription factor signaling during pregnancy disrupts the induction of efflux transporters in type I diabetic mice.

METHODS

Type I diabetes was induced in female C57BL/6 mice with multiple low dose intraperitoneal injections of streptozotocin (STZ) at least 2 weeks prior to mating with normoglycemic male mice. On gestation day 14, livers were collected from vehicle- and STZ-treated non-pregnant and pregnant mice for quantification of efflux transporter and transcription factor signaling.

RESULTS

STZ treatment up-regulated expression of Mrp1-5, Mdr1, Abcg5, Abcg8, Bcrp, and Bsep mRNA and/or protein in the livers of non-pregnant mice. Interestingly, little to no change in transporter expression was observed in STZ-treated pregnant mice compared to vehicle- and STZ-treated non-pregnant mice.

CONCLUSIONS

This study demonstrates the opposing regulation of hepatobiliary efflux transporters in response to diabetes and pregnancy and points to PPARγ, Nrf2, and FXR as candidate pathways underlying the differential expression of transporters.

Molecular mechanisms of hypolipidemic effects of curcumin

Recent evidence suggests potential benefits from phytochemicals and micronutrients in reducing the elevated oxidative and lipid-mediated stress associated with inflammation, obesity, and atherosclerosis. These compounds may either directly scavenge reactive oxygen or nitrogen species or they may modulate the activity of signal transduction enzymes leading to changes in the expression of antioxidant genes. Alternatively, they may reduce plasma lipid levels by modulating lipid metabolic genes in tissues and thus reduce indirectly lipid-mediated oxidative and endoplasmic reticulum stress through their hypolipidemic effect. Here we review the proposed molecular mechanisms by which curcumin, a polyphenol present in the rhizomes of turmeric (Curcuma longa) spice, influences oxidative and lipid-mediated stress in the vascular system. At the molecular level, mounting experimental evidence suggests that curcumin may act chemically as scavenger of free radicals and/or influences signal transduction (e.g., Akt, AMPK) and modulates the activity of specific transcription factors (e.g., FOXO1/3a, NRF2, SREBP1/2, CREB, CREBH, PPARγ, and LXRα) that regulate the expression of genes involved in free radicals scavenging (e.g., catalase, MnSOD, and heme oxygenase-1) and lipid homeostasis (e.g., aP2/FABP4, CD36, HMG-CoA reductase, and carnitine palmitoyltransferase-I (CPT-1)). At the cellular level, curcumin may induce a mild oxidative and lipid-metabolic stress leading to an adaptive cellular stress response by hormetic stimulation of these cellular antioxidant defense systems and lipid metabolic enzymes. The resulting lower oxidative and lipid-mediated stress may not only explain the beneficial effects of curcumin on inflammation, cardiovascular, and neurodegenerative disease, but may also contribute to the increase in maximum life-span observed in animal models.

Enhanced Nrf2 activity worsens insulin resistance, impairs lipid accumulation in adipose tissue, and increases hepatic steatosis in leptin-deficient mice

The study herein determined the role of nuclear factor erythoid 2-related factor 2 (Nrf2) in the pathogenesis of hepatic steatosis, insulin resistance, obesity, and type 2 diabetes. Lep(ob/ob)-Keap1-knockdown (KD) mice, which have increased Nrf2 activity, were generated. Markers of obesity and type 2 diabetes were measured in C57Bl/6J, Keap1-KD, Lep(ob/ob), and Lep(ob/ob)-Keap1-KD mice. Lep(ob/ob)-Keap1-KD mice exhibited less lipid accumulation, smaller adipocytes, decreased food intake, and reduced lipogenic gene expression. Enhanced Nrf2 activity impaired insulin signaling, prolonged hyperglycemia in response to glucose challenge, and induced insulin resistance in Lep(ob/ob) background. Nrf2 augmented hepatic steatosis and increased lipid deposition in liver. Next, C57Bl/6J and Keap1-KD mice were fed a high-fat diet (HFD) to determine whether Keap1 and Nrf2 impact HFD-induced obesity. HFD-induced obesity and lipid accumulation in white adipose tissue was decreased in Keap1-KD mice. Nrf2 activation via Keap1-KD or sulforaphane suppressed hormone-induced differentiation and decreased peroxisome proliferator-activated receptor-γ, CCAAT/enhancer-binding protein α, and fatty acid-binding protein 4 expression in mouse embryonic fibroblasts. Constitutive Nrf2 activation inhibited lipid accumulation in white adipose tissue, suppressed adipogenesis, induced insulin resistance and glucose intolerance, and increased hepatic steatosis in Lep(ob/ob) mice.

Dysregulated expression of fatty acid oxidation enzymes and iron-regulatory genes in livers of Nrf2-null mice

BACKGROUND AND AIM

Hepatic excessive iron may play a role in the pathogenesis of non-alcoholic steatohepatitis (NASH). Nrf2 is a master regulator of antioxidative responses. However, the role of Nrf2 in lipid and iron homeostasis remains unclear. Accordingly, it was examined how Nrf2 regulates lipid-related and iron-regulatory genes after feeding a high-fat diet (HFD) with iron.

METHODS

Wild-type and Nrf2-null mice were fed the following diets: (i) control diet (4% soybean oil) for 12 weeks, (ii) control diet for 8 weeks followed by control diet containing 0.5% carbonyl iron for 4 weeks, (iii) HFD (4% soybean oil and 16% lard) for 12 weeks, (iv) HFD for 8 weeks followed by HFD containing 0.5% carbonyl iron for 4 weeks. Blood and livers were removed after 12 weeks.

RESULTS

Nrf2-null control mice exhibited a tendency towards higher hepatic triglycerides compared to wild-type control mice. Hepatic malondialdehyde was higher and hepatic iron levels tended to be higher in Nrf2-null mice than wild-type counterparts while on a HFD. The HFD with iron synergistically induced mRNA expression of Pparα targets, including Acox and Cpt1 in wild-type mice, yet the induction was diminished in Nrf2-null mice. Hepatic hepcidin and ferroportin 1 mRNA expression were increased in wild-type mice after feeding a HFD with iron, but were unchanged in any group of Nrf2-null mice.

CONCLUSIONS

Nrf2 deletion dysregulates hepatic mRNA expression of β-oxidation enzymes and iron-related genes, possibly causing a trend for increased hepatic triglyceride and iron concentrations. Nrf2 may have roles in the progression of NASH.

Myeloid deletion of nuclear factor erythroid 2-related factor 2 increases atherosclerosis and liver injury

OBJECTIVE

To determine the impact of hematopoietic deletion of nuclear factor- (erythroid-derived 2) like 2 factor (Nrf2) on the development of atherosclerosis and liver injury in an obese, hypercholesterolemic mouse model.

METHODS AND RESULTS

Two-month-old male low-density lipoprotein receptor-deficient mice were lethally irradiated and transplanted with either wild type or Nrf2-deficient (Nrf2(-/-)) bone marrow cells. At 3 months of age, mice were placed on an obesogenic high-fat diet (HFD), high-cholesterol diet for 7 months. Despite no differences in body weight, body fat percentage, liver fat, plasma glucose, lipids, or insulin, the HFD-fed Nrf2(-/-) bone marrow recipients had increased proinflammatory vascular gene expression, a significant increase in atherosclerosis area (18% versus 28%; P=0.018) and lesion complexity, and a marked increase in liver fibrosis. The acceleration of vascular and liver injury may arise from enhanced macrophage migration, inflammation, and oxidative stress resulting from myeloid Nrf2 deficiency.

CONCLUSIONS

Myeloid-derived Nrf2 activity attenuates atherosclerosis development and liver inflammation and fibrosis associated with obesity. Prevention of oxidative stress in macrophage and other myeloid lineage cells may be an important therapeutic target to reduce inflammation-driven complications of obesity.

NAD(P)H:quinone oxidoreductase 1 activity reduces hypertrophy in 3T3-L1 adipocytes

The nuclear factor E2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap1) pathway responds to oxidative stress via control of several antioxidant defense gene expressions. Recent efforts demonstrate that Nrf2 modulates development of adiposity and adipogenesis. One of the major Nrf2-regulated proteins, NAD(P)H:quinone oxidoreductase 1 (NQO1), is implicated in the development of adipose tissue and obesity. However, little is known about in situ disposition of Nrf2, Keap1, and NQO1 during adipogenesis in isolated adipocytes. Based on literature data, we hypothesized that adipocyte differentiation would increase expression of the Nrf2/Keap1 pathway and NQO1. Using murine 3T3-L1 preadipocytes, we mapped an increase in NQO1 protein at limited clonal expansion and postmitotic growth arrest (Days 1-3) stages and a decrease in terminally differentiated (Day 8) adipocytes that lasted for several days afterward. Conversely, NQO1, Nrf2, and Keap1 mRNA expressions were all increased in differentiated adipocytes (Days 11-14), indicating a discrepancy between steady-state mRNA levels and resulting protein. Treatment of differentiated 3T3-L1 adipocytes with glycogen synthase kinase-3β (GSK-3β) inhibitor, LiCl, led to 1.9-fold increase in NQO1 protein. Sulforaphane enhanced NQO1 protein (10.5-fold) and blunted triglyceride and FABP4 accumulation. The decrement in triglyceride content was partially reversed when NQO1 activity was pharmacologically inhibited. These data demonstrate a biphasic response of Nrf2 and NQO1 during adipocyte differentiation that is regulated by Keap1- and GSK-3β-dependent mechanisms, and that hypertrophy is negatively regulated by NQO1 activity.

Bardoxolone methyl decreases megalin and activates nrf2 in the kidney

Inflammation and oxidative stress are hallmarks and mediators of the progression of CKD. Bardoxolone methyl, a potent activator of the nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated antioxidant and anti-inflammatory response, increases estimated GFR and decreases BUN, serum phosphorus, and uric acid concentrations in patients with moderate to severe CKD. However, it also increases albuminuria, which is associated with inflammation and disease progression. Therefore, we investigated whether this bardoxolone methyl-induced albuminuria may result from the downregulation of megalin, a protein involved in the tubular reabsorption of albumin and lipid-bound proteins. Administration of bardoxolone methyl to cynomolgus monkeys significantly decreased the protein expression of renal tubular megalin, which inversely correlated with the urine albumin-to-creatinine ratio. Moreover, daily oral administration of bardoxolone methyl to monkeys for 1 year did not lead to any adverse effects on renal histopathologic findings but did reduce serum creatinine and BUN, as observed in patients with CKD. Finally, the bardoxolone methyl-induced decrease in megalin corresponded with pharmacologic induction of renal Nrf2 targets, including NAD(P)H:quinone oxidoreductase 1 enzyme activity and glutathione content. This result indicates that Nrf2 may have a role in megalin regulation. In conclusion, these data suggest that the increase in albuminuria that accompanies bardoxolone methyl administration may result, at least in part, from reduced expression of megalin, which seems to occur without adverse effects and with strong induction of Nrf2 targets.

Therapeutic administration of the direct thrombin inhibitor argatroban reduces hepatic inflammation in mice with established fatty liver disease

Thrombin generation is increased in patients with nonalcoholic fatty liver disease (NAFLD) and in mouse models of diet-induced obesity. Deficiency in the thrombin receptor protease activated receptor-1 reduces hepatic inflammation and steatosis in mice fed a Western diet. However, it is currently unclear whether thrombin inhibitors can modify the pathogenesis of established NAFLD. We tested the hypothesis that thrombin inhibition could reverse hepatic steatosis and inflammation in mice with established diet-induced NAFLD. Low-density lipoprotein receptor-deficient LDLr(-/-) mice were fed a control diet or a Western diet for 19 weeks. Mice were given the direct thrombin inhibitor argatroban ∼15 mg/kg/day or its vehicle via a miniosmotic pump for the final 4 weeks of the study. Argatroban administration significantly reduced hepatic proinflammatory cytokine expression and reduced macrophage and neutrophil accumulation in livers of mice fed a Western diet. Argatroban did not significantly impact hepatic steatosis, as indicated by histopathology, Oil Red O staining, and hepatic triglyceride levels. Argatroban reduced serum triglyceride and cholesterol levels in mice fed a Western diet. Argatroban reduced both α-smooth muscle actin expression and Type 1 collagen mRNA levels in livers of mice fed a Western diet, indicating reduced activation of hepatic stellate cells. This study indicates that therapeutic intervention with a thrombin inhibitor attenuates hepatic inflammation and several profibrogenic changes in mice fed a Western diet.

The Nrf2-antioxidant response element pathway: a target for regulating energy metabolism

The nuclear factor E2-related factor 2 (Nrf2) is a transcription factor that responds to oxidative stress by binding to the antioxidant response element (ARE) in the promoter of genes coding for antioxidant enzymes like NAD(P)H:quinone oxidoreductase 1 and proteins for glutathione synthesis. The Nrf2/ARE pathway has nutritional interest owing to its activation by phytochemicals such as sulforaphane. Recently, the Nrf2 pathway was identified as having regulatory functions in mitochondrial biogenesis, adipocyte differentiation and liver energy metabolism. Activation of Nrf2 increases energy metabolism and conversely suppresses lipid synthesis. Lard-based, but not soybean oil-based, high-fat diets reduce mRNA expression of Nrf2 and its downstream targets, suggesting a macronutrient influence on the activation of the Nrf2 pathway and susceptibility to oxidative stress. This review examines data revealing the Nrf2 pathway's regulatory role in energy metabolism at the molecular, cellular and whole animal levels. Understanding the relationship of Nrf2 and energy metabolism in cells, tissues and physiologic systems will provide novel insights for nutritional interventions for obesity and its comorbidities such as diabetes.

NF-E2-related factor 1 (Nrf1) serves as a novel regulator of hepatic lipid metabolism through regulation of the Lipin1 and PGC-1β genes

Hepatic lipid metabolism is under elaborate regulation, and perturbations in this regulatory process at the transcriptional level lead to pathological conditions. NF-E2-related factor 1 (Nrf1) is a member of the cap'n'collar (CNC) transcription factor family. Hepatocyte-specific Nrf1 gene conditional-knockout mice are known to develop hepatic steatosis, but it remains unclear how Nrf1 contributes to the lipid homeostasis. Therefore, in this study we examined the gene expression profiles of Nrf1-deficient mouse livers. A pathway analysis based on the profiling results revealed that the levels of expression of the genes related to lipid metabolism, amino acid metabolism, and mitochondrial respiratory function were decreased in Nrf1-deficient mouse livers, indicating the profound effects that the Nrf1 deficiency conferred to various metabolic pathways. We discovered that the Nrf1 deficiency leads to the reduced expression of the transcriptional coactivator genes Lipin1 and PGC-1β (for peroxisome proliferator-activated receptor γ coactivator 1β). Chromatin immunoprecipitation analyses showed that Nrf1 binds to the antioxidant response elements (AREs) in regulatory regions of the Lipin1 and PGC-1β genes and the binding of Nrf1 to the AREs activates reporter gene transcription. These results thus identified Nrf1 to be a novel regulator of the Lipin1 and PGC-1β genes, providing new insights into the Nrf1 function in hepatic lipid metabolism.

Farnesoid X receptor induces murine scavenger receptor Class B type I via intron binding

Farnesoid X receptor (FXR) is a nuclear receptor and a key regulator of liver cholesterol and triglyceride homeostasis. Scavenger receptor class B type I (SR-BI) is critical for reverse cholesterol transport (RCT) by transporting high-density lipoprotein (HDL) into liver. FXR induces SR-BI, however, the underlying molecular mechanism of this induction is not known. The current study confirmed induction of SR-BI mRNA by activated FXR in mouse livers, a human hepatoma cell line, and primary human hepatocytes. Genome-wide FXR binding analysis in mouse livers identified 4 putative FXR response elements in the form of inverse repeat separated by one nucleotide (IR1) at the first intron and 1 IR1 at the downstream of the mouse Sr-bi gene. ChIP-qPCR analysis revealed FXR binding to only the intronic IR1s, but not the downstream one. Luciferase assays and site-directed mutagenesis further showed that 3 out of 4 IR1s were able to activate gene transcription. A 16-week high-fat diet (HFD) feeding in mice increased hepatic Sr-bi gene expression in a FXR-dependent manner. In addition, FXR bound to the 3 bona fide IR1s in vivo, which was increased following HFD feeding. Serum total and HDL cholesterol levels were increased in FXR knockout mice fed the HFD, compared to wild-type mice. In conclusion, the Sr-bi/SR-BI gene is confirmed as a FXR target gene in both mice and humans, and at least in mice, induction of Sr-bi by FXR is via binding to intronic IR1s. This study suggests that FXR may serve as a promising molecular target for increasing reverse cholesterol transport.