Oxidative and electrophilic stresses activate Nrf2 through inhibition of ubiquitination activity of Keap1

Mathematical modeling reveals quantitative properties of KEAP1-NRF2 signaling

Under oxidative and electrophilic stresses, cells launch an NRF2-mediated transcriptional antioxidant program. The activation of NRF2 depends on a redox sensor, KEAP1, which promotes the ubiquitination and degradation of NRF2. While a great deal has been learned about this duo, its quantitative signaling properties are largely unexplored. Here we examined these properties, including half-life, maximal activation, and response steepness (ultrasensitivity) of NRF2, through mathematical modeling. The models describe the binding of KEAP1 and NRF2 via ETGE and DLG motifs, NRF2 production, KEAP1-dependent and independent NRF2 degradation, and perturbations by different classes of NRF2 activators. Simulations revealed at the basal condition, NRF2 is sequestered by KEAP1 and the KEAP1-NRF2 complex is distributed comparably in an ETGE-bound (open) state and an ETGE and DLG dual-bound (closed) state. When two-step ETGE binding is considered, class I–V, electrophilic NRF2 activators shift the balance to a closed state incompetent to degrade NRF2, while the open and closed KEAP1-NRF2 complexes transition from operating in cycle mode to equilibrium mode. Ultrasensitive NRF2 activation (a steep rise of free NRF2) can occur when NRF2 nearly saturates KEAP1. The ultrasensitivity results from zero-order degradation through DLG binding and protein sequestration through ETGE binding. Optimal abundances of cytosolic and nuclear KEAP1 exist to maximize ultrasensitivity. These response characteristics do not require disruption of DLG binding as suggested by the hinge-latch hypothesis. In comparison, class VI NRF2 activators cause a shift to the open KEAP1-NRF2 complex and ultimately its complete dissociation, resulting in a fast release of NRF2 followed by stabilization. However, ultrasensitivity is lost due to decreasing free KEAP1 abundance. In summary, by simulating the dual role of KEAP1, i.e., sequestering and promoting degradation of NRF2, our modeling provides novel quantitative insights into NRF2 activation, which may help design novel NRF2 modulators and understand the oxidative actions of environmental stressors.

•

Steep (ultrasensitive) NRF2 activation can occur when it rises to saturate KEAP1.

•

Ultrasensitivity results from zero-order degradation and protein sequestration.

•

Optimal cytosolic and nuclear KEAP1 abundances exist for maximal ultrasensitivity.

•

Open and closed KEAP1-NRF2 complexes transition in cycle and equilibrium mode.

•

NRF2 activation by KEAP1-NRF2 interaction inhibitors is more gradual.

Nrf2 and Heme Oxygenase-1 Involvement in Atherosclerosis Related Oxidative Stress

Atherosclerosis remains the underlying process responsible for cardiovascular diseases and the high mortality rates associated. This chronic inflammatory disease progresses with the formation of occlusive atherosclerotic plaques over the inner walls of vascular vessels, with oxidative stress being an important element of this pathology. Oxidation of low-density lipoproteins (ox-LDL) induces endothelial dysfunction, foam cell activation, and inflammatory response, resulting in the formation of fatty streaks in the atherosclerotic wall. With this in mind, different approaches aim to reduce oxidative damage as a strategy to tackle the progression of atherosclerosis. Special attention has been paid in recent years to the transcription factor Nrf2 and its downstream-regulated protein heme oxygenase-1 (HO-1), both known to provide protection against atherosclerotic injury. In the current review, we summarize the involvement of oxidative stress in atherosclerosis, focusing on the role that these antioxidant molecules exert, as well as the potential therapeutic strategies applied to enhance their antioxidant and antiatherogenic properties.

Nrf2 Mutation/Activation Is Dispensable for the Development of Chemically Induced Mouse HCC

BACKGROUND & AIMS

Activation of the kelch-like ECH-associated protein 1 (Keap1)-nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway has been associated with metabolic reprogramming in many tumors, including hepatocellular carcinoma (HCC). However, the contribution of Nrf2 mutations in this process remains elusive. Here, we investigated the occurrence of Nrf2 mutations in distinct models of mouse hepatocarcinogenesis.

METHODS

HCCs were generated by experimental protocols consisting of the following: (1) a single dose of diethylnitrosamine (DEN), followed by repeated treatments with the nuclear-receptor agonist 1,4-bis-[2-(3,5-dichloropyridyloxy)]benzene; (2) repeated treatments with 1,4-bis-[2-(3,5-dichloropyridyloxy)]benzene alone; (3) a single dose of DEN followed by exposure to a choline-deficient L-amino acid-defined diet; and (4) a single dose of DEN with no further treatment. All of these protocols led to HCC development within 28-42 weeks. Activation of the Keap1-Nrf2 pathway was investigated by analyzing the presence of Nrf2 gene mutations, and the expression of Nrf2 target genes. Metabolic reprogramming was assessed by evaluating the expression of genes involved in glycolysis, the pentose phosphate pathway, and glutaminolysis.

RESULTS

No Nrf2 mutations were found in any of the models of hepatocarcinogenesis analyzed. Intriguingly, despite the described cooperation between β-catenin and the Nrf2 pathway, we found no evidence of Nrf2 activation in both early dysplastic nodules and HCCs, characterized by the presence of up to 80%-90% β-catenin mutations. No HCC metabolic reprogramming was observed either.

CONCLUSIONS

These results show that, unlike rat hepatocarcinogenesis, Nrf2 mutations do not occur in 4 distinct models of chemically induced mouse HCC. Interestingly, in the same models, metabolic reprogramming also was minimal or absent, supporting the concept that Nrf2 activation is critical for the switch from oxidative to glycolytic metabolism.

Angelica Polysaccharide Antagonizes 5-FU-Induced Oxidative Stress Injury to Reduce Apoptosis in the Liver Through Nrf2 Pathway

Oxidative stress induced by chemotherapeutic agents causes hepatotoxicity. 5-Fluorouracil (5-FU) has been found to have a variety of side effects, but its toxic effect on the liver and the mechanism are still unclear. Angelica polysaccharide (ASP), the main active ingredient of Dang Gui, has antioxidative stress effects. In this study, we investigated the antagonistic effects of ASP on 5-FU-induced injury in the mouse liver and human normal liver cell line MIHA and the possible mechanism. Our results show that ASP inhibited 5-FU-induced the decrease in Bcl-2 protein and the increase in Bax protein. ASP alleviated 5-FU-induced the increase in alanine aminotransferase (ALT), triglyceride (TG), and aspartate aminotransferase (AST) content; hepatic steatosis; and liver fibrosis. ASP restored 5-FU-induced swelling of mitochondria and the endoplasmic reticulum. 5-FU promoted the expression of Keap1 and increased the binding to NF-E2-related factor 2 (Nrf2) to reduce the nuclear translocation of Nrf2, thereby weakening the transcriptional activity of Nrf2 to inhibit the expression of HO-1; reducing the activity of GSH, SOD, and CAT to increase ROS content; and aggravating DNA damage (indicated by the increase in 8-OHdG). However, ASP reversed these reactions. In conclusion, ASP attenuated the 5-FU-induced Nrf2 pathway barrier to reduce oxidative stress injury and thereby inhibit the disorder of lipid anabolism and apoptosis. The study provides a new protectant for reducing the hepatic toxicity caused by 5-FU and a novel target for treating the liver injury.

Steatotic Hepatocytes Release Mature VLDL Through Methionine and Tyrosine Metabolism in a Keap1-Nrf2-Dependent Manner

BACKGROUND AND AIMS

NAFLD is a lipotoxic disease wherein hepatic steatosis and oxidative stress are key pathogenic features. However, whether free amino acids (FAAs) are associated with the oxidative stress response against lipotoxicity has yet to be determined. We hypothesized that an imbalance of FAAs aggravates hepatic steatosis by interfering with the oxidative stress sensor.

APPROACH AND RESULTS

C57BL/6 mouse immortalized hepatocytes, primary hepatocytes, and organoids were employed. Steatotic hepatocytes treated with oleic acid (OA) were cultured under FAA-modifying media based on the concentrations of FAAs in the hepatic portal blood of wild-type (WT) mice. As in vivo experiments, WT hepatocyte-specific Kelch-like ECH-associated protein 1 (Keap1) knockout mice (Keap1^∆hepa ) and Cre- control mice (Keap1^fx/fx ) were fed high-fat (HF) diets with modified amino acid content. The correlations were analyzed between the areas of lipid droplets (LDs) around central vein and plasma OA/FAA ratio in 61 patients with NAFLD. Mice fed an HF, Met-restricted, and tyrosine (Tyr)-deficient diet showed the NAFLD-like phenotype in which the nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2), triglyceride-rich VLDL, and fumarate were decreased in liver, but Keap1^∆hepa ameliorated these phenomena. Reactive oxygen species and LDs induced by the deprivation of Met and Tyr were prevented in hepatic organoids generated from Keap1^∆hepa . Dimethyl fumarate, an Nrf2 inducer, ameliorated the steatosis and increased the hepatic fumarate reduced by the deprivation of Met and Tyr in vitro. OA/Met or Tyr ratio in peripheral blood was associated with the hepatic steatosis in patients with NAFLD.

CONCLUSIONS

An imbalance between free fatty acids and Met and Tyr induces hepatic steatosis by disturbing the VLDL assembling through the Keap1-Nrf2 system.

Role of Nrf2 in Synaptic Plasticity and Memory in Alzheimer's Disease

Nuclear factor erythroid 2-related factor 2 (Nrf2) is an important transcription factor that reduces oxidative stress. When reactive oxygen species (ROS) or reactive nitrogen species (RNS) are detected, Nrf2 translocates from the cytoplasm into the nucleus and binds to the antioxidant response element (ARE), which regulates the expression of antioxidant and anti-inflammatory genes. Nrf2 impairments are observed in the majority of neurodegenerative disorders, including Alzheimer’s disease (AD). The classic hallmarks of AD include β-amyloid (Aβ) plaques, and neurofibrillary tangles (NFTs). Oxidative stress is observed early in AD and is a novel therapeutic target for the treatment of AD. The nuclear translocation of Nrf2 is impaired in AD compared to controls. Increased oxidative stress is associated with impaired memory and synaptic plasticity. The administration of Nrf2 activators reverses memory and synaptic plasticity impairments in rodent models of AD. Therefore, Nrf2 activators are a potential novel therapeutic for neurodegenerative disorders including AD.

Molecular mechanisms of pulmonary carcinogenesis by polycyclic aromatic hydrocarbons (PAHs): Implications for human lung cancer

Lung cancer has the second highest incidence and highest mortality compared to all other cancers. Polycyclic aromatic hydrocarbon (PAH) molecules belong to a class of compounds that are present in tobacco smoke, diesel exhausts, smoked foods, as well as particulate matter (PM). PAH-derived reactive metabolites are significant contributors to lung cancer development. The formation of these reactive metabolites entails metabolism of the parent PAHs by cytochrome P4501A1/1B1 (CYP1A1/1B1) and epoxide hydrolase enzymes. These reactive metabolites then react with DNA to form DNA adducts, which contribute to key gene mutations, such as the tumor suppressor gene, p53 and are linked to pulmonary carcinogenesis. PAH exposure also leads to upregulation of CYP1A1 transcription by binding to the aryl hydrocarbon receptor (AHR) and eliciting transcription of the CYP1A1 promoter, which comprises specific xenobiotic-responsive element (XREs). While hepatic and pulmonary CYP1A1/1B1 metabolize PAHs to DNA-reactive metabolites, the hepatic CYP1A2, however, may protect against lung tumor development by suppressing both liver and lung CYP1A1 enzymes. Further analysis of these enzymes has shown that PAH-exposure also induces sustained transcription of CYP1A1, which is independent of the persistence of the parent PAH. CYP1A2 enzyme plays an important role in the sustained induction of hepatic CYP1A1. PAH exposure may further contribute to pulmonary carcinogenesis by producing epigenetic alterations. DNA methylation, histone modification, long interspersed nuclear element (LINE-1) activation, and non-coding RNA, specifically microRNA (miRNA) alterations may all be induced by PAH exposure. The relationship between PAH-induced enzymatic reactive metabolite formation and epigenetic alterations is a key area of research that warrants further exploration. Investigation into the potential interplay between these two mechanisms may lead to further understanding of the mechanisms of PAH carcinogenesis. These mechanisms will be crucial for the development of effective targeted therapies and early diagnostic tools.

Cisplatin synergizes with PRLX93936 to induce ferroptosis in non-small cell lung cancer cells

Ferroptosis is a newly identified type of regulated cell death that is affected by lipid peroxidation and reactive oxygen species (ROS). In the current study, we showed that cisplatin and PRLX93936, an analog of erastin that has been tested in clinical trials, demonstrated synergistic effects against non-small cell lung cancer (NSCLC) cells. Cotreatment with cisplatin and PRLX93936 induced ferroptosis, as evidenced by the upregulation of ROS, lipid peroxidation and Fe²⁺. Further investigation revealed that cotreatment with cisplatin and PRLX93936 inhibited GPX4 and that overexpression of GPX4 prevented cell death. Moreover, the Nrf2/Keap1 pathway also regulated the sensitivity to cisplatin and PRLX93936 in NSCLC cells. Nrf2 silencing increased this sensitivity while inhibition of Keap1 attenuated it. Overall, our data reveal a new effective treatment for NSCLC by synergizing cisplatin and PRLX93936 to induce ferroptosis.

New insights into the mechanism of Keap1-Nrf2 interaction based on cancer-associated mutations

AIMS

Keap1-Nrf2 signaling pathway is one of the most important antioxidant signaling pathways, and its abnormal activation is related to cancer metastasis and drug resistance. Many studies have shown Keap1 and Nrf2 mutations are closely associated with cancer occurrence. However, few studies focus on Keap1-Nrf2 binding characteristics of cancer-associated mutations. The study investigated the molecular mechanism between Keap1/Nrf2 mutations and cancer.

MAIN METHODS

We have determined the crystal structure of the Keap1-Kelch domain with Nrf2 25-mer peptide. What's more, we clarified the molecular effects of Nrf2^Thr80 and Nrf2^Pro85 on the binding of Keap1 by the method isothermal titration calorimetry (ITC), differential scanning fluorimetry (DSF) and electrophoretic mobility shift assay (EMSA). Especially, we confirmed the effect of Thr80 and Pro85 mutations on Keap1/Nrf2 signaling pathway in HEK293T cells by RT-PCR and western blot (WB). Finally, we verified the effect of six cancer-related high-frequency somatic mutations Keap1^G364C, Keap1^D422N, Keap1^R470C, Keap1^G480W, Keap1^E493Q and Keap1^R601L on binding with Nrf2 through ITC experiments.

KEY FINDINGS

Nrf2^Thr80 and Nrf2^Pro85 play a vital role in the Keap1-Nrf2 interaction. Mutant or modification at position Thr80 will disrupt the interaction. Especially, Nrf2^Thr80 and Nrf2^Pro85 mutations activate the expression of cytoprotective genes in HEK293T cells. As for Keap1, except G364C, the binding affinity of other cancer-related mutants to Nrf2 hardly changed, which means that Keap1 mutants can activate Nrf2 without disrupting the binding to Nrf2.

SIGNIFICANCE

The study provides new insight into Keap1/Nrf2 signaling pathway and cancer.

(-)-Epigallocatechin-3-O-gallate at a high concentration may induce lipolysis via ATP consumption by activation of stress defense mechanisms

Green tea catechins have thus far been demonstrated to have antiobesity effects in a variety of experimental models. However, upstream molecular events triggering those phenomena remain to be identified. In this study, we found that (-)-epigallocatechin-3-O-gallate (EGCG) promoted lipolysis in lipid-loaded Huh7 human hepatoma cells. Notably, EGCG at a high concentration induced both oxidative stress and protein stress (proteo-stress), leading to activation of stress defense mechanisms, such as mRNA expressions of antioxidant and phase-2 detoxifying enzymes, and heat shock proteins. Furthermore, EGCG decreased the level of intracellular ATP, while glucose uptake from culture media was promoted possibly for energy homeostasis. EGCG also upregulated the expression of adipose triglyceride lipase, and activated AMP-activated protein kinase. Collectively, these results suggest that EGCG induces lipolysis to compensate for ATP reduction derived from activation of stress defense systems against its oxidative and proteo-stress properties.

Effects of fatty acid nitroalkanes on signal transduction pathways and airway macrophage activation

Fatty acid nitroalkenes are reversibly-reactive electrophiles that are endogenously detectable at nM concentrations and display anti-inflammatory, pro-survival actions. These actions are elicited through the alteration of signal transduction proteins via a Michael addition on nucleophilic cysteine thiols. Nitrated fatty acids (NO2-FAs), like 9- or 10-nitro-octadec-9-enolic acid, will act on signal transduction proteins directly or on key regulatory proteins to cause an up-regulation or down-regulation of the protein's expression, yielding an anti-inflammatory response. These responses have been characterized in many organ systems, such as the cardiovascular system, with the pulmonary system less well defined. Macrophages are one of the most abundant immune cells in the lung and are essential in maintaining lung homeostasis. Despite this, macrophages can play a role in both acute and chronic lung injury due to up-regulation of anti-inflammatory signal transduction pathways and down-regulation of pro-inflammatory pathways. Through their propensity to alter signal transduction pathways, NO2-FAs may be able to reduce macrophage activation during pulmonary injury. This review will focus on the implications of NO2-FAs on macrophage activation in the lung and the signal transduction pathways that may be altered, leading to reduced pulmonary injury.

Skeletal Muscle Nrf2 Contributes to Exercise-Evoked Systemic Antioxidant Defense Via Extracellular Vesicular Communication

This review explores the hypothesis that the repetitive contraction-relaxation that occurs during chronic exercise activates skeletal myocyte nuclear factor erythroid-derived 2-like 2 (Nrf2) to upregulate antioxidant enzymes. These proteins are secreted into the circulation within extracellular vesicles and taken up by remote cells, thus providing remote organs with cytoprotection against subsequent oxidative stress.

Targeting NRF2 to treat cancer

NRF2 is a basic leucine zipper (bZip) transcription factor that is the master regulator of redox homeostasis. Under basal conditions, the cellular level of NRF2 is low due to a posttranslational regulation by the ubiquitin proteasome system (UPS). But, when an organism is challenged with oxidative or xenobiotic stress, the NRF2 pathway is activated by inhibition of the E3 ubiquitin ligase complex that normally marks NRF2 for destruction. For several decades, researchers have searched for molecules that can intentionally activate NRF2, as this was shown to be a means to prevent certain diseases, at least in animal models. In the present era, there are many compounds known to activate the NRF2 pathway including natural products and synthetic compounds, covalent and non-covalent compounds, and others. However, it was also revealed that like many protective pathways, the NRF2 pathway has a dark side. Just as NRF2 can protect normal cells from damage, it can protect malignant cells from damage. As cells transform, they are exposed to many stressors and aberrant upregulation of NRF2 can facilitate transformation and it can help cancer cells to grow, to spread, and to resist treatment. For this reason, researchers are also interested in the discovery and development of NRF2 inhibitors. In the present review, we will begin with a general discussion of NRF2 structure and function, we will discuss the latest in NRF2 non-covalent activators, and we will discuss the current state of NRF2 inhibitors.

An integrated approach for assessing the in vitro and in vivo redox-related effects of nanomaterials

Over the last few decades, nanotechnology has risen to the forefront of both the research and industrial interest, resulting in the manufacture and utilization of various nanomaterials, as well as in their integration into a wide range of fields. However, the consequent elevated exposure to such materials raises serious concerns regarding their effects on human health and safety. Existing scientific data indicate that the induction of oxidative stress, through the excessive generation of Reactive Oxygen Species (ROS), might be the principal mechanism of exerting their toxicity. Meanwhile, a number of nanomaterials exhibit antioxidant properties, either intrinsic or resulting from their functionalization with conventional antioxidants. Considering that their redox properties are implicated in the manifestation of their biological effects, we propose an integrated approach for the assessment of the redox-related activities of nanomaterials at three biological levels (in vitro-cell free systems, cell cultures, in vivo). Towards this direction, a battery of translational biomarkers is recommended, and a series of reliable protocols are presented in detail. The aim of the present approach is to acquire a better understanding with respect to the biological actions of nanomaterials in the interrelated fields of Redox Biology and Toxicology.

Takotsubo Syndrome: Impact of endothelial dysfunction and oxidative stress

Takotsubo Syndrome (TTS) is characterized by a transient left ventricular dysfunction recovering spontaneously within days or weeks. Although the pathophysiology of TTS remains obscure, there is growing evidence suggesting TTS to be associated with increased production of reactive oxygen species (ROS), which may be involved in causing transient coronary and peripheral endothelial dysfunction leading to a transient impairment of myocardial contraction due to stunning (apical ballooning). Endothelial dysfunction is mainly caused by decreased vascular and myocardial nitric oxide bioavailability in response to increased ROS production. Accordingly, studies in humans and animal models demonstrated increased myocardial dihydroethidium staining of the myocardium in endomyocardial biopsy specimens, increased levels of hydrogen peroxide and malondialdehyde as well as reduced glutathione levels compatible with increased oxidative stress. As significant superoxide sources the mitochondria and the NADPH oxidase isoform NOX-4 and the NOX-2 regulating cytosolic subunit p67phox have been identified. Treatment with antioxidants such as sodium hydrosulfide reduced superoxide production in mitochondria and reduced expression of NOX-4 and p67phox, respectively. The presence of superoxide and nitric oxide also provides the basis for the concept of nitro-oxidative as well as nitrosative stress in TTS.

Functional Polymorphism in the NFE2L2 Gene Associated With Tuberculosis Susceptibility

Background

Nuclear transcription factor erythroid 2 p45-related factor 2 (Nrf2), encoded by NFE2L2, functions as a key transcription factor and regulates expression of antioxidant genes. Our study aimed to investigate the association of single nucleotide polymorphisms of NFE2L2 with tuberculosis (TB) and latent tuberculosis infection (LTBI) and the underlying causal mechanisms.

Methods

1950 unrelated Chinese Han participants were included in our two independent study groups. Five tag polymorphisms were selected and genotyped. The functional effects of the rs13005431 polymorphism were confirmed by dual-luciferase reporter assays and mRNA level comparisons.

Results

Rs13005431_C and rs2364723_G were associated with increased TB susceptibility (P = 0.010 and P = 0.041) after adjustment for confounding factors. rs6726395_A was associated with increased risk of active TB (P=0.035) in a comparison with the LTBI group. The frequency of haplotype rs1049751- rs13005431 AC was higher in the TB group (P =0.013), while frequency of haplotype AT was higher in the healthy control group (P =0.025). The luciferase activity of a plasmid with the rs13005431C-promoter was significantly lower than that of the rs13005431T-promoter. In addition, neutrophils with the CC/TC genotypes which were activated by GM-CSF showed a decreased level of NFE2L2 mRNA when compared with the rs13005431 TT genotype.

Conclusions

Our study suggests that allele C of rs13005431 might increase the susceptibility to TB by down-regulating the transcriptional activity of NFE2L2.

Aldo-keto reductase inhibitors increase the anticancer effects of tyrosine kinase inhibitors in chronic myelogenous leukemia

Tyrosine kinase inhibitors (TKIs) are widely utilized in clinical practice to treat carcinomas, but secondary tumor resistance during chronic treatment can be problematic. AKR1B1 and AKR1B10 of the aldo-keto reductase (AKR) superfamily are highly expressed in cancer cells and are believed to be involved in drug resistance. The aim of this study was to understand how TKI treatment of chronic myelogenous leukemia (CML) cells changes their glucose metabolism and if inhibition of AKRs can sensitize CML cells to TKIs. K562 cells were treated with the TKIs imatinib, nilotinib, or bosutinib, and the effects on glucose metabolism, cell death, glutathione levels, and AKR levels were assessed. To assess glucose dependence, cells were cultured in normal and low-glucose media. Pretreatment with AKR inhibitors, including epalrestat, were used to determine AKR-dependence. Treatment with TKIs increased intracellular glucose, AKR1B1/10 levels, glutathione oxidation, and nuclear translocation of nuclear factor erythroid 2-related factor 2, but with minimal cell death. These effects were dependent on intracellular glucose accumulation. Pretreatment with epalrestat, or a selective inhibitor of AKR1B10, exacerbated TKI-induced cell death, suggesting that especially AKR1B10 was involved in protection against TKIs. Thus, by disrupting cell protective mechanisms, AKR inhibitors may render CML more susceptible to TKI treatments.

Mitochondrial Reactive Oxygen Species and Their Contribution in Chronic Kidney Disease Progression Through Oxidative Stress

Mitochondria are known to generate approximately 90% of cellular reactive oxygen species (ROS). The imbalance between mitochondrial reactive oxygen species (mtROS) production and removal due to overproduction of ROS and/or decreased antioxidants defense activity results in oxidative stress (OS), which leads to oxidative damage that affects several cellular components such as lipids, DNA, and proteins. Since the kidney is a highly energetic organ, it is more vulnerable to damage caused by OS and thus its contribution to the development and progression of chronic kidney disease (CKD). This article aims to review the contribution of mtROS and OS to CKD progression and kidney function deterioration.

Stabilization of Nrf2 leading to HO-1 activation protects against zinc oxide nanoparticles-induced endothelial cell death

With the abundant production and wide application of zinc oxide nanoparticles (ZnONPs), the potential health risks of ZnONPs have raised serious concerns. Oxidative stress is recognized as the most important outcome of the toxicity induced by ZnONPs. The Nrf2-Keap1 system and its downstream antioxidative genes are the fundamental protective mechanisms for redox hemeostasis. However, the detailed mechanisms of Nrf2 activation in ZnONPs-treated endothelial cells and murine blood vessels have yet to be elucidated. Herein, we show that Nrf2 was activated and played a negative role in cell death induced by ZnONPs. Moreover, we demonstrate that HO-1 was the most extensively upregulated antioxidative gene-activated by Nrf2. Forced overexpression of HO-1, pharmacological activation of HO-1 with the agonists RTA-408 (omaveloxolone, an FDA-approved drug) and RTA-402 repressed cell death, and treatment with HO-1 antagonist SnPP exacerbated the cell death. Importantly, loss of HO-1 diminished the cytoprotective role induced by Nrf2 in ZnONPs-treated HUVEC cells, indicating that the Nrf2-HO-1 axis was the crucial regulatory mechanism for the antioxidative response in the context of ZnONPs-induced endothelial damage. Mechanistically, we demonstrate that the p62-Keap1 axis was not involved in the activation of Nrf2. Intriguingly, the degradation half-life of Nrf2 in HUVEC cells was increased from less than 1 h under quiescent conditions to approximately 6 h under ZnONPs treatment condition; moreover, ZnONPs treatment induced activation of Nrf2/HO-1 and accumulation of ubiquitin in the aorta ventralis of mouse, suggesting that the ubiquitin-proteasome system had been perturbed, which subsequently led to the stabilization of Nrf2 and activation of HO-1. This study might contribute to a better understanding of ZnONPs-associated toxicity.

Harnessing the cardiovascular benefits of exercise: are Nrf2 activators useful?

The ability of physical activity to ameliorate cardiovascular disease and improve cardiovascular health is well accepted, but many aspects of the molecular mechanisms underlying these benefits are incompletely understood. Exercise increases the levels of reactive oxygen species (ROS) through various mechanisms. This triggers the activation of Nrf2, a redox-sensitive transcription factor activated by increases in oxidative stress. Activation of Nrf2 mitigates oxidative stress by increasing the nuclear transcription of many antioxidant genes while also mediating additional beneficial effects through the cytoprotective nature of Nrf2 signaling. Understanding the transcriptional patterns of Nrf2 caused by exercise can help in the design of pharmacological mimicry of the process in patients who are unable to exercise for various reasons.

Reconciling the Biological and Transcriptional Variability of Hepatoblastoma with Its Mutational Uniformity

Simple Summary

Hepatoblastoma (HB), the most common form of childhood liver cancer, is associated with dual mutation and/or dysregulation of the Wnt/β-catenin and Hippo pathways in ~50% of cases. However, this mutational simplicity cannot explain HB’s biological and histologic diversity. This discussion focuses upon recent work showing that specific β-catenin mutants are key determinants of this HB variability as well as their metabolic and transcriptional signatures. Dysregulation of the anti-oxidant NFE2L2 pathway also contributes to tumorigenesis by being directly transforming in association with either of the other two factors. The transcriptional overlap of tumors generated by pairs of factors identifies crucial targets that likely mediate HB tumorigenesis, behavior and appearance.

Abstract

Hepatoblastoma (HB), the most common childhood liver cancer, is associated with seven distinct histologic subtypes and variable degrees of clinical aggressiveness and presentation. Yet it is among the least genomically altered tumors known, with about half of HBs showing mutation and/or dysregulation of the Wnt/β-catenin and Hippo pathways. This raises the question of how this mutational simplicity can generate such biological and histologic complexity. Recent work shows that the identity of the underlying β-catenin mutation is a major contributor. Mutation or over-expression of the NFE2L2/NRF2 transcription factor, previously thought only to promote anti-oxidant responses, has also recently been shown to accelerate the growth of HBs generated by mutations in the Wnt/β-catenin and Hippo pathways while imparting novel features such as the tumor-associated cysts and necrosis. Moreover, patient-associated NFE2L2 mutations are overtly transforming when co-expressed with either mutant β-catenin or a Hippo pathway effector. The finding that tumorigenesis can be driven by any two arms of the β-catenin/Hippo/NFE2L2 axis has permitted the identification of a small subset of coordinately regulated tumor-specific transcripts, some of whose levels correlate with inferior long-term outcomes in HB and other cancers. Collectively, these findings begin to provide for more refined and molecularly based classification, survival algorithms and design of chemotherapeutic regimens.

Crosstalk between endoplasmic reticulum stress and oxidative stress: a dynamic duo in multiple myeloma

Under physiological and pathological conditions, cells activate the unfolded protein response (UPR) to deal with the accumulation of unfolded or misfolded proteins in the endoplasmic reticulum. Multiple myeloma (MM) is a hematological malignancy arising from immunoglobulin-secreting plasma cells. MM cells are subject to continual ER stress and highly dependent on the UPR signaling activation due to overproduction of paraproteins. Mounting evidence suggests the close linkage between ER stress and oxidative stress, demonstrated by overlapping signaling pathways and inter-organelle communication pivotal to cell fate decision. Imbalance of intracellular homeostasis can lead to deranged control of cellular functions and engage apoptosis due to mutual activation between ER stress and reactive oxygen species generation through a self-perpetuating cycle. Here, we present accumulating evidence showing the interactive roles of redox homeostasis and proteostasis in MM pathogenesis and drug resistance, which would be helpful in elucidating the still underdefined molecular pathways linking ER stress and oxidative stress in MM. Lastly, we highlight future research directions in the development of anti-myeloma therapy, focusing particularly on targeting redox signaling and ER stress responses.

Extracts of Jasminum sambac flowers fermented by Lactobacillus rhamnosus inhibit H2 O2 - and UVB-induced aging in human dermal fibroblasts

Ultraviolet (UV) irradiation is a crucial factor that leads to skin photoaging and results in increased DNA damage, oxidative stress, and collagen degradation. Jasmine flowers have been utilized as a traditional medicine in Asia to treat various diseases, including dermatitis, diarrhea, and fever. Furthermore, the fermented broth of Lactobacillus rhamnosus has been reported to exert protective effects on the skin. In the present study, jasmine flower extract was fermented with L. rhamnosus. We investigated the antioxidant and collagen-promoting effects on UVB/H₂ O₂ -induced HS68 dermal fibroblast cell damage. The results indicated that treatment with the fermented flower extracts of Jasminum sambac (F-FEJS) could enhance the viability of HS68 cells. Furthermore, the UVB/H₂ O₂ -induced excessive production of reactive oxygen species, degradation of collagen, activation of MAPKs, including P38, ERK, and JNK, and premature senescence were remarkably attenuated by F-FEJS in dermal fibroblast cells. The nuclear accumulation of p-c-jun, which is downstream of MAPK, and the inactivation of p-smad2/3, which is one of the crucial transcription factors that enhance collagen synthesis, were reversed in response to F-FEJS treatment in UVB/H₂ O₂ -exposed cells. Notably, the expression of antioxidant genes, such as HO-1, and the nuclear translocation of Nrf2 were further enhanced by F-FEJS in UVB/H₂ O₂ -treated cells. Interestingly, the F-FEJS-induced increase in ARE luciferase activity indicated the activation of Nrf2/ARE signaling. In conclusion, our findings demonstrated that F-FEJS can effectively ameliorate UVB/H₂ O₂ -induced dermal cell aging and may be considered a promising ingredient in skin aging therapy.

Transcriptional Analyses of Acute Exposure to Methylmercury on Erythrocytes of Loggerhead Sea Turtle

To understand changes in enzyme activity and gene expression as biomarkers of exposure to methylmercury, we exposed loggerhead turtle erythrocytes (RBCs) to concentrations of 0, 1, and 5 mg L-1 of MeHg and de novo transcriptome were assembled using RNA-seq. The analysis of differentially expressed genes (DEGs) indicated that 79 unique genes were dysregulated (39 upregulated and 44 downregulated genes). The results showed that MeHg altered gene expression patterns as a response to the cellular stress produced, reflected in cell cycle regulation, lysosomal activity, autophagy, calcium regulation, mitochondrial regulation, apoptosis, and regulation of transcription and translation. The analysis of DEGs showed a low response of the antioxidant machinery to MeHg, evidenced by the fact that genes of early response to oxidative stress were not dysregulated. The RBCs maintained a constitutive expression of proteins that represented a good part of the defense against reactive oxygen species (ROS) induced by MeHg.

SUMO-Modification of Human Nrf2 at K110 and K533 Regulates Its Nucleocytoplasmic Localization, Stability and Transcriptional Activity

BACKGROUND/AIMS

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that binds to the antioxidant response element(s) (ARE) in target gene promoters, enabling oxidatively stressed cells to respond in order to restore redox homeostasis. Post-translational modifications (PTMs) that mediate activation of Nrf2, in the cytosol and its release from Keap1, have been extensively studied but PTMs that impact its biology after activation are beginning to emerge. In this regard, PTMs like acetylation, phosphorylation, ubiquitination and sumoylation contribute towards the Nrf2 subcellular localization, and its transactivation function. We previously demonstrated that Nrf2 traffics to the promyelocytic leukemia-nuclear bodies (PML-NB), where it is a target for modification by small ubiquitin-like modifier (SUMO) proteins (sumoylation), but the site(s) for SUMO conjugation have not been determined. In this study, we aim to identify SUMO-2 conjugation site(s) and explore the impact, sumoylation of the site(s) have on Nrf2 stability, nuclear localization and transcriptional activation of its target gene expression upon oxidative stress.

METHODS

The putative SUMO-binding sites in Nrf2 for human isoform1 (NP_006155.2) and mouse homolog (NP_035032.1) were identified using a computer-based SUMO-predictive software (SUMOplot™). Site-directed mutagenesis, immunoblot analysis, and ARE-mediated reporter gene assays were used to assess the impact of sumoylation on these site(s) in vitro. Effect of mutation of these sumoylation sites of Nrf2 on expression of Heme Oxygenase1 (HO-1) was determined in HEK293T cell.

RESULTS


Eight putative sumoylation sites were identified by SUMOplot™ analysis. Out of the eight predicted sites only one 532LKDE535 of human (h) and its homologous 524LKDE527 of mouse (m) Nrf2, exactly matches the SUMO-binding consensus motif. The other high probability SUMO-acceptor site identified was residue K110, in the motifs 109PKSD112 and 109PKQD112 of human and mouse Nrf2, respectively. Mutational analysis of putative sumoylation sites (human (h)/mouse (m)
K110, hK533 and mK525) showed that these residues are needed for SUMO-2 conjugation, nuclear localization and ARE driven transcription of reporter genes and the endogenous HO-1 expression by Nrf2. These residues also stabilized Nrf2, as evident from shorter half-lives of the mutant protein compared to wild-type Nrf2.

CONCLUSION

Our findings indicate that SUMO-2
mediated sumoylation of K110 and K533 in human Nrf2 regulates in part its transcriptional activity by enhancing its stabilization and nuclear localization.

The signaling pathway PI3K/Akt/Nrf2/HO-1 plays a role in the mitochondrial protection promoted by astaxanthin in the SH-SY5Y cells exposed to hydrogen peroxide

The mitochondria are the major source of reactive species in the mammalian cells. Hydrogen peroxide (H₂O₂) is a potent inducer of redox impairment by a mechanism, at least in part, dependent on its ability to impair mitochondrial function. H₂O₂ plays an important role in several pathological conditions, including neurodegeneration and cardiovascular diseases. Astaxanthin (AST) is a xanthophyll that may be found in microalgae, crustaceans, and salmon and exhibits antioxidant and anti-inflammatory effects in different cell types. Even though there is evidence pointing to a role for AST as mitochondrial protectant agent, it was not clearly demonstrated how this xanthophyll attenuates mitochondrial stress. Therefore, we investigated here whether and how AST would be able to prevent the H₂O₂-induced mitochondrial dysfunction in the human neuroblastoma SH-SY5Y cells. We found that AST (20 μM) prevented the H₂O₂-induced loss of mitochondrial membrane potential (MMP) and decrease in the activity of the Complexes I and V. AST pretreatment blocked the mitochondria-related pro-apoptotic effects elicited by H₂O₂. AST upregulated the enzyme heme oxygenase-1 (HO-1) and the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) by a mechanism dependent on the phosphoinositide 3-kinase/Akt (PI3K/Akt) signaling pathway. Inhibition of the PI3K/Akt or of the HO-1 enzyme abolished the AST-induced mitochondrial protection in cells challenged with H₂O₂. Silencing of Nrf2 caused similar effects. Thus, we suggest that AST promotes mitochondrial protection by a mechanism dependent on the PI3K/Akt/Nrf2/HO-1 signaling pathway in SH-SY5Y cells exposed to H₂O₂.

Therapeutic Targeting of the NRF2 Signaling Pathway in Cancer

Cancer is one of the most fatal diseases with an increasing incidence and mortality all over the world. Thus, there is an urgent need for novel therapies targeting major cancer-related pathways. Nuclear factor-erythroid 2-related factor 2 (NRF2) and its major negative modulator Kelch-like ECH-associated protein 1 (KEAP1) are main players of the cellular defense mechanisms against internal and external cell stressors. However, NRF2/KEAP1 signaling pathway is dysregulated in various cancers, thus promoting tumor cell survival and metastasis. In the present review, we discuss the mechanisms of normal and deregulated NRF2 signaling pathway focusing on its cancer-related functions. We further explore activators and inhibitors of this pathway as cancer targeting drug candidates in order to provide an extensive background on the subject.

The antioxidant response favors Leishmania parasites survival, limits inflammation and reprograms the host cell metabolism

The oxidative burst generated by the host immune system can restrict intracellular parasite entry and growth. While this burst leads to the induction of antioxidative enzymes, the molecular mechanisms and the consequences of this counter-response on the life of intracellular human parasites are largely unknown. The transcription factor NF-E2-related factor (NRF2) could be a key mediator of antioxidant signaling during infection due to the entry of parasites. Here, we showed that NRF2 was strongly upregulated in infection with the human Leishmania protozoan parasites, its activation was dependent on a NADPH oxidase 2 (NOX2) and SRC family of protein tyrosine kinases (SFKs) signaling pathway and it reprogrammed host cell metabolism. In inflammatory leishmaniasis caused by a viral endosymbiont inducing TNF-α in chronic leishmaniasis, NRF2 activation promoted parasite persistence but limited TNF-α production and tissue destruction. These data provided evidence of the dual role of NRF2 in protecting both the invading pathogen from reactive oxygen species and the host from an excess of the TNF-α destructive pro-inflammatory cytokine.

Molecular mechanisms associated with oxidative damage in the mouse testis induced by LaCl3

China is the world's largest rare earth producer and exporter, previous studies have shown that rare earth elements can cause oxidative damage in animal testis. However, the molecular mechanisms underlying these observations have yet to be elucidated. In this paper, male mice were fed with different doses (10, 20, and 40 mg/kg BW) of LaCl₃ for 90 consecutive days, regulatory role of nuclear factor erythroid-2 related factor 2 (Nrf-2)/antioxidant response element (ARE) pathway in testicular oxidative stress induced by LaCl₃ were investigated. Analysis showed that LaCl₃ exposure could lead to severe testicular pathological changes and apoptosis in spermatogenic cells, it up-regulated the peroxidation of lipids, proteins and DNA, and induced the excessive levels of reactive oxygen species (ROS) production in mouse testis, reduced the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and glutathione S epoxide transferase (GST) as well as the glutathione (GSH) content. Furthermore, exposure to LaCl₃ also downregulated the expression of Nrf2 and its target gene products, including heme oxygenase 1 (HO-1), glutamate-cysteine ligase catalytic subunit (GCLC), NAD(P)H dehydrogenase [quinine] 1(NQO1), protein kinase C (PKC), and phosphatidylinositol 3-kinase (PI3K), but upregulated the expression of Kelch-like ECH-related protein 1 (Keap1) in damaged mouse testes. Collectively, our data imply that the oxidative damage induced by LaCl₃ in testis was related to inhibition of the Nrf-2/AREs pathway activation.

Shufeng Jiedu capsules protect rats against LPS-induced acute lung injury via activating NRF2-associated antioxidant pathway

Shufeng Jiedu capsule (SFJDC) is a traditional Chinese medicine, which has been used for the treatment of respiratory infections for more than thirty years in Hunan (China). SFJDC protected rats against LPS-induced acute lung injury (ALI); however, the molecular mechanisms underlying the therapeutic effects of SFJDC remain unclear. Therefore, this study aimed at analyzing the major anti-inflammatory compounds of SFJDC and exploring the underlying molecular mechanisms. SFJDC dissolved in water was fingerprinted by UPLC/Q-TOF. Inflammation response was assessed by histopathological examination and ELISA assay. Arterial blood gases were also analyzed to evaluate the function of rat lungs. The expression levels of Kelch-like ECH-associating protein 1 (Keap1), Nrf2, heme oxygenase-1 (HO1), Cullin 3 (CUL3) and NQO1 were analyzed by Western blotting. Results indicated that SFJDC alleviated inflammation response by reducing the level of inflammatory cytokines, and upregulation of glutathione-S-transferase (GST) and superoxide dismutase (SOD) in lung tissues. Furthermore, SFJDC suppressed LPS-induced upregulation of Keap 1 and CUL3 in rat lungs. The expression of NRF2 HO1 and NQO1 were further upregulated by SFJDC in the presence of LPS, indicating that SFJDC might activate the NRF2-associated antioxidant pathway. In conclusion, SFJDC treatment may protect the rat lungs from LPS by alleviating the inflammation response via NRF2-associated antioxidant pathway.

Ameliorative potentials of Persea americana leaf extract on toxicants - induced oxidative assault in multiple organs of wistar albino rat

Background

Persea americana (PA) is a popular medicinal plant in folkloric medicines. The present study therefore investigates the ameliorative potentials of its leaves extract on carbon tetrachloride and rifampicin-induced toxicity in the liver, kidney and heart of albino rat. This was aimed at assessing the potentials of the plant in the management of liver, kidney and heart diseases.

Methodology

Forty (40) rats were randomly divided into eight (8) groups of five animals each. Groups I and II were administered with only distilled water and carbon tetrachloride (CCl4) respectively. Groups III and IV animals received 3.0 ml/kg bw of CCl4 and were treated with the extract at 50 mg/kg bw and 100 mg/kg respectively, while group V received 100 mg/kg bw. of silymarin orally for 14 days. Groups VI animals were administered with rifampicin (250 mg/kg bw.) only, while groups VII and VIII animals received rifampicin and were treated with 50 mg and 100 mg/kg bw of the extract respectively. Activities of creatine kinase, aspartate amino transferase, alanine amino transferase, alkaline phosphatase, superoxide dismutase, catalase as well as levels of urea, uric acid, bilirubin and malonidialdehyde (MDA) were assayed. Lipid profiles and histopathological examination of liver and kidney slices were also performed.

Result

Treatment with P. americana significantly (p < 0.05) restored all deranged biochemical parameters (creatine kinase, aspartate amino transferase, alanine amino transferase, alkaline phosphatase, urea, uric acid, bilirubin, MDA, lipid profile as well as superoxide dismutase and catalase) in a dose-dependent manner. Normal hepatic and renal histoarchitecture were also restored following treatment with P. americana.

Conclusion

Amelioration of distorted cardiac, hepatic and renal histoarchitecture as well as restoration of lipid profile, biomarkers of liver and kidney injury and antioxidant enzymes (catalase and superoxide dismutase) affirm the potential usefulness of P. americana in the management of liver, kidney and heart diseases.

Targeted de-repression of neuronal Nrf2 inhibits α-synuclein accumulation

Many neurodegenerative diseases are associated with neuronal misfolded protein accumulation, indicating a need for proteostasis-promoting strategies. Here we show that de-repressing the transcription factor Nrf2, epigenetically shut-off in early neuronal development, can prevent protein aggregate accumulation. Using a paradigm of α-synuclein accumulation and clearance, we find that the classical electrophilic Nrf2 activator tBHQ promotes endogenous Nrf2-dependent α-synuclein clearance in astrocytes, but not cortical neurons, which mount no Nrf2-dependent transcriptional response. Moreover, due to neuronal Nrf2 shut-off and consequent weak antioxidant defences, electrophilic tBHQ actually induces oxidative neurotoxicity, via Nrf2-independent Jun induction. However, we find that epigenetic de-repression of neuronal Nrf2 enables them to respond to Nrf2 activators to drive α-synuclein clearance. Moreover, activation of neuronal Nrf2 expression using gRNA-targeted dCas9-based transcriptional activation complexes is sufficient to trigger Nrf2-dependent α-synuclein clearance. Thus, targeting reversal of the developmental shut-off of Nrf2 in forebrain neurons may alter neurodegenerative disease trajectory by boosting proteostasis.

Patient-Derived Mutant Forms of NFE2L2/NRF2 Drive Aggressive Murine Hepatoblastomas

BACKGROUND & AIMS

Hepatoblastoma (HB), the most common pediatric liver cancer, often bears β-catenin mutations and deregulates the Hippo tumor suppressor pathway. Murine HBs can be generated by co-expressing β-catenin mutants and the constitutively active Hippo effector YAP^S127A. Some HBs and other cancers also express mutants of NFE2L2/NRF2 (NFE2L2), a transcription factor that tempers oxidative and electrophilic stress. In doing so, NFE2L2 either suppresses or facilitates tumorigenesis.

METHODS

We evaluated NFE2L2's role in HB pathogenesis by co-expressing all combinations of mutant β-catenin, YAP^S127A, and the patient-derived NFE2L2 mutants L30P and R34P in murine livers. We evaluated growth, biochemical and metabolic profiles, and transcriptomes of the ensuing tumors.

RESULTS

In association with β-catenin+YAP^S127A, L30P and R34P markedly accelerated HB growth and generated widespread cyst formation and necrosis, which are otherwise uncommon features. Surprisingly, any 2 members of the mutant β-catenin-YAP^S127A-L30P/R34P triad were tumorigenic, thus directly establishing NFE2L2's oncogenicity. Each tumor group displayed distinct features but shared 22 similarly deregulated transcripts, 10 of which perfectly correlated with survival in human HBs and 17 of which correlated with survival in multiple adult cancers. One highly up-regulated transcript encoded serpin E1, a serine protease inhibitor that regulates fibrinolysis, growth, and extracellular matrix. Although the combination of mutant β-catenin, YAP^S127A, and serpin E1 did not accelerate cystogenic tumor growth, it did promote the widespread necrosis associated with mutant β-catenin-YAP^S127A-L30P/R34P tumors.

CONCLUSIONS

Our findings establish the direct oncogenicity of NFE2L2 mutants and key transcripts, including serpin E1, that drive specific HB features.

Dietary iso-α-acids prevent acetaldehyde-induced liver injury through Nrf2-mediated gene expression

Acetaldehyde is the major toxic metabolite of alcohol (ethanol) and enhances fibrosis of the liver through hepatic stellate cells. Additionally, alcohol administration causes the accumulation of reactive oxygen species (ROS), which induce hepatocyte injury-mediated lipid peroxidation. Iso-α-acids, called isohumulones, are bitter acids in beer. The purpose of this study was to investigate the protective effects of iso-α-acids against alcoholic liver injury in hepatocytes in mice. C57BL/6N mice were fed diets containing isomerized hop extract, which mainly consists of iso-α-acids. After 7 days of feeding, acetaldehyde was administered by a single intraperitoneal injection. The acetaldehyde-induced increases in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were suppressed by iso-α-acids intake. Hepatic gene expression analyses showed the upregulation of detoxifying enzyme genes, glutathione-S-transferase (GST) and aldehyde dehydrogenase (ALDH). In vitro, iso-α-acids upregulated the enzymatic activities of GST and ALDH and induced the nuclear translocation of nuclear factor-erythroid-2-related factor 2 (Nfe2l2; Nrf2), a master regulator of antioxidant and detoxifying systems. These results suggest that iso-α-acid intake prevents acetaldehyde-induced liver injury by reducing oxidative stress via Nrf2-mediated gene expression.

Fumonisin B1 alters global m6A RNA methylation and epigenetically regulates Keap1-Nrf2 signaling in human hepatoma (HepG2) cells

FB₁ is a common contaminant of cereal grains that affects human and animal health. It has become increasingly evident that epigenetic changes are implicated in FB₁ toxicity. N6-methyladenosine (m6A), the most abundant post-transcriptional RNA modification, is influenced by fluctuations in redox status. Since oxidative stress is a characteristic of FB₁ exposure, we determined if there is cross-talk between oxidative stress and m6A in FB₁-exposed HepG2 cells. Briefly, HepG2 cells were treated with FB₁ (0, 5, 50, 100, 200 µM; 24 h) and ROS, LDH and m6A levels were quantified. qPCR was used to determine the expression of m6A modulators, Nrf2, Keap1 and miR-27b, while western blotting was used to quantify Keap1 and Nrf2 protein expression. Methylation status of Keap1 and Nrf2 promoters was assessed and RNA immunoprecipitation quantified m6A-Keap1 and m6A-Nrf2 levels. FB₁ induced accumulation of intracellular ROS (p ≤ 0.001) and LDH leakage (p ≤ 0.001). Elevated m6A levels (p ≤ 0.05) were accompanied by an increase in m6A "writers" [METLL3 (p ≤ 0.01) and METLL14 (p ≤ 0.01)], and "readers" [YTHDF1 (p ≤ 0.01), YTHDF2 (p ≤ 0.01), YTHDF3 (p ≤ 0.001) and YTHDC2 (p ≤ 0.01)] and a decrease in m6A "erasers" [ALKBH5 (p ≤ 0.001) and FTO (p ≤ 0.001)]. Hypermethylation and hypomethylation occurred at Keap1 (p ≤ 0.001) and Nrf2 (p ≤ 0.001) promoters, respectively. MiR-27b was reduced (p ≤ 0.001); however, m6A-Keap1 (p ≤ 0.05) and m6A-Nrf2 (p ≤ 0.01) levels were upregulated. This resulted in the ultimate decrease in Keap1 (p ≤ 0.001) and increase in Nrf2 (p ≤ 0.001) expression. Our findings reveal that m6A RNA methylation can be modified by exposure to FB₁, and a cross-talk between m6A and redox regulators does occur.

1-O-Hexyl-2,3,5-Trimethylhydroquinone Ameliorates the Development of Preeclampsia through Suppression of Oxidative Stress and Endothelial Cell Apoptosis

1-O-Hexyl-2,3,5-trimethylhydroquinone (HTHQ), a potent nuclear factor-E2-related factor 2 (Nrf2) activator, has potent antioxidant activity by scavenging reactive oxygen species (ROS). However, the role of HTHQ on the development of preeclampsia (PE) and the underlying mechanisms have barely been explored. In the present study, PE model was induced by adenovirus-mediated overexpression of soluble fms-like tyrosine kinase 1 (sFlt-1) in pregnant mice. The results showed that HTHQ treatment significantly relieved the high systolic blood pressure (SBP) and proteinuria and increased the fetal weight and fetal weight/placenta weight in preeclamptic mice. Furthermore, we found that HTHQ treatment significantly decreased soluble endoglin (sEng), endothelin-1 (ET-1), and activin A and restored vascular endothelial growth factor (VEGF) in preeclamptic mice. In addition, HTHQ treatment inhibited oxidative stress and endothelial cell apoptosis by increasing the levels of Nrf2 and its downstream haemoxygenase-1 (HO-1) protein. In line with the data in vivo, we discovered that HTHQ treatment attenuated oxidative stress and cell apoptosis in human umbilical vein endothelial cells (HUVECs) following hypoxia and reperfusion (H/R), and the HTHQ-mediated protection was lost after transfected with siNrf2. In conclusion, these results suggested that HTHQ ameliorates the development of preeclampsia through suppression of oxidative stress and endothelial cell apoptosis.

Upstream Regulator Analysis of Wooden Breast Myopathy Proteomics in Commercial Broilers and Comparison to Feed Efficiency Proteomics in Pedigree Male Broilers

In an effort to understand the apparent trade-off between the continual push for growth performance and the recent emergence of muscle pathologies, shotgun proteomics was conducted on breast muscle obtained at ~8 weeks from commercial broilers with wooden breast (WB) myopathy and compared with that in pedigree male (PedM) broilers exhibiting high feed efficiency (FE). Comparison of the two proteomic datasets was facilitated using the overlay function of Ingenuity Pathway Analysis (IPA) (Qiagen, CA, USA). We focused on upstream regulator analysis and disease-function analysis that provides predictions of activation or inhibition of molecules based on (a) expression of downstream target molecules, (b) the IPA scientific citation database. Angiopoeitin 2 (ANGPT2) exhibited the highest predicted activation Z-score of all molecules in the WB dataset, suggesting that the proteomic landscape of WB myopathy would promote vascularization. Overlaying the FE proteomics data on the WB ANGPT2 upstream regulator network presented no commonality of protein expression and no prediction of ANGPT2 activation. Peroxisome proliferator coactivator 1 alpha (PGC1α) was predicted to be inhibited, suggesting that mitochondrial biogenesis was suppressed in WB. PGC1α was predicted to be activated in high FE pedigree male broilers. Whereas RICTOR (rapamycin independent companion of mammalian target of rapamycin) was predicted to be inhibited in both WB and FE datasets, the predictions were based on different downstream molecules. Other transcription factors predicted to be activated in WB muscle included epidermal growth factor (EGFR), X box binding protein (XBP1), transforming growth factor beta 1 (TGFB1) and nuclear factor (erythroid-derived 2)-like 2 (NFE2L2). Inhibitions of aryl hydrocarbon receptor (AHR), AHR nuclear translocator (ARNT) and estrogen related receptor gamma (ESRRG) were also predicted in the WB muscle. These findings indicate that there are considerable differences in upstream regulators based on downstream protein expression observed in WB myopathy and in high FE PedM broilers that may provide additional insight into the etiology of WB myopathy.

Development of a Homogeneous Time-Resolved Fluorescence Resonance Energy Transfer (TR-FRET) Assay for the Inhibition of Keap1-Nrf2 Protein-Protein Interaction

The transcription factor, nuclear factor erythroid 2-related factor 2 (Nrf2), plays a major role in regulating the antioxidant defense system through the Kelch-like ECH-associated protein 1-Nrf2-antioxidant response element (Keap1-Nrf2-ARE) pathway. Small-molecule inhibitors targeting Keap1-Nrf2 protein-protein interaction (PPI) decrease the rate of Nrf2 degradation by the 26S proteasome and thus increase the intracellular level of Nrf2, which translocates into the nucleus, leading to upregulated expression of cytoprotective and antioxidant enzymes. Such inhibitors can be developed into potential preventive and therapeutic agents of diseases caused by oxidative damage. To more effectively identify promising Nrf2 activators through the inhibition of Keap1-Nrf2 PPI, a homogeneous time-resolved fluorescence resonance energy transfer (TR-FRET) assay was developed in this work by indirectly labeling the Keap1 Kelch domain protein with Tb-anti-His antibody as the donor and using, as the acceptor, fluorescein isothiocyanate (FITC)-labeled 9mer Nrf2 peptide amide, the same fluorescent probe that was used in an earlier fluorescence polarization (FP) assay. Assay conditions, including concentrations of the various components, buffer type, and incubation time, were optimized in the TR-FRET competition assay with known small-molecule inhibitors of Keap1-Nrf2 PPI. Under the optimized conditions, the Keap1-Nrf2 TR-FRET assay exhibited great sensitivity with a high dynamic range and considerable stability for as long as 5 h. The Z' factor was determined to be 0.82, suggesting that the assay is suitable for high-throughput screening and lead optimization of inhibitors of Keap1-Nrf2 PPI. Furthermore, the TR-FRET assay is capable of differentiating potent inhibitors of Keap1-Nrf2 PPI down to the subnanomolar inhibition constant (Ki) range.

DIA-based systems biology approach unveils E3 ubiquitin ligase-dependent responses to a metabolic shift

The yeast Saccharomyces cerevisiae is a powerful model system for systems-wide biology screens and large-scale proteomics methods. Nearly complete proteomics coverage has been achieved owing to advances in mass spectrometry. However, it remains challenging to scale this technology for rapid and high-throughput analysis of the yeast proteome to investigate biological pathways on a global scale. Here we describe a systems biology workflow employing plate-based sample preparation and rapid, single-run, data-independent mass spectrometry analysis (DIA). Our approach is straightforward, easy to implement, and enables quantitative profiling and comparisons of hundreds of nearly complete yeast proteomes in only a few days. We evaluate its capability by characterizing changes in the yeast proteome in response to environmental perturbations, identifying distinct responses to each of them and providing a comprehensive resource of these responses. Apart from rapidly recapitulating previously observed responses, we characterized carbon source-dependent regulation of the GID E3 ligase, an important regulator of cellular metabolism during the switch between gluconeogenic and glycolytic growth conditions. This unveiled regulatory targets of the GID ligase during a metabolic switch. Our comprehensive yeast system readout pinpointed effects of a single deletion or point mutation in the GID complex on the global proteome, allowing the identification and validation of targets of the GID E3 ligase. Moreover, this approach allowed the identification of targets from multiple cellular pathways that display distinct patterns of regulation. Although developed in yeast, rapid whole-proteome-based readouts can serve as comprehensive systems-level assays in all cellular systems.

3-Allyltrisulfanyl-alanine Formation during the Preparation of Aged Garlic Extract

The formation of 3-allyltrisulfanyl-alanine (ATrSA) was investigated during the aging process to prepare aged garlic extract (AGE). In raw garlic, ATrSA and its possible precursor, S-allylmercaptocysteine (SAMC), were barely detectable. However, the ATrSA content in AGE increased steadily during the 22 month of aging, while the SAMC level increased to a maximum at 4 months and then gradually decreased. In a model reaction mimicking the AGE preparation process, ATrSA production was decreased when the formation of SAMC was blocked by a γ-glutamyl-transpeptidase inhibitor but its decrease was reversed by the addition of SAMC. We also found that ATrSA was formed by the incubation of SAMC with allylsulfides such as diallyldisulfide and diallyltrisulfide. These findings suggest that ATrSA is formed via the reaction involving SAMC during the aging process. In addition, we found that ATrSA inhibits the secretion of interleukin-6 induced by lipopolysaccharide in mouse splenic lymphocytes in culture.

NRF2 and the Ambiguous Consequences of Its Activation during Initiation and the Subsequent Stages of Tumourigenesis

NF-E2 p45-related factor 2 (NRF2, encoded in the human by NFE2L2) mediates short-term adaptation to thiol-reactive stressors. In normal cells, activation of NRF2 by a thiol-reactive stressor helps prevent, for a limited period of time, the initiation of cancer by chemical carcinogens through induction of genes encoding drug-metabolising enzymes. However, in many tumour types, NRF2 is permanently upregulated. In such cases, its overexpressed target genes support the promotion and progression of cancer by suppressing oxidative stress, because they constitutively increase the capacity to scavenge reactive oxygen species (ROS), and they support cell proliferation by increasing ribonucleotide synthesis, serine biosynthesis and autophagy. Herein, we describe cancer chemoprevention and the discovery of the essential role played by NRF2 in orchestrating protection against chemical carcinogenesis. We similarly describe the discoveries of somatic mutations in NFE2L2 and the gene encoding the principal NRF2 repressor, Kelch-like ECH-associated protein 1 (KEAP1) along with that encoding a component of the E3 ubiquitin-ligase complex Cullin 3 (CUL3), which result in permanent activation of NRF2, and the recognition that such mutations occur frequently in many types of cancer. Notably, mutations in NFE2L2, KEAP1 and CUL3 that cause persistent upregulation of NRF2 often co-exist with mutations that activate KRAS and the PI3K-PKB/Akt pathway, suggesting NRF2 supports growth of tumours in which KRAS or PKB/Akt are hyperactive. Besides somatic mutations, NRF2 activation in human tumours can occur by other means, such as alternative splicing that results in a NRF2 protein which lacks the KEAP1-binding domain or overexpression of other KEAP1-binding partners that compete with NRF2. Lastly, as NRF2 upregulation is associated with resistance to cancer chemotherapy and radiotherapy, we describe strategies that might be employed to suppress growth and overcome drug resistance in tumours with overactive NRF2.

Environmental pollutants and the immune response

Environmental pollution is one of the most serious challenges to health in the modern world. Pollutants alter immune responses and can provoke immunotoxicity. In this Review, we summarize the major environmental pollutants that are attracting wide-ranging concern and the molecular basis underlying their effects on the immune system. Xenobiotic receptors, including the aryl hydrocarbon receptor (AHR), sense and respond to a subset of environmental pollutants by activating the expression of detoxification enzymes to protect the body. However, chronic activation of the AHR leads to immunotoxicity. KEAP1-NRF2 is another important system that protects the body against environmental pollutants. KEAP1 is a sensor protein that detects environmental pollutants, leading to activation of the transcription factor NRF2. NRF2 protects the body from immunotoxicity by inducing the expression of genes involved in detoxification, antioxidant and anti-inflammatory activities. Intervening in these sensor-response systems could protect the body from the devastating immunotoxicity that can be induced by environmental pollutants.

Modulation of Inflammation and Immune Responses by Heme Oxygenase-1: Implications for Infection with Intracellular Pathogens

Heme oxygenase-1 (HO-1) catalyzes the degradation of heme molecules releasing equimolar amounts of biliverdin, iron and carbon monoxide. Its expression is induced in response to stress signals such as reactive oxygen species and inflammatory mediators with antioxidant, anti-inflammatory and immunosuppressive consequences for the host. Interestingly, several intracellular pathogens responsible for major human diseases have been shown to be powerful inducers of HO-1 expression in both host cells and in vivo. Studies have shown that this HO-1 response can be either host detrimental by impairing pathogen control or host beneficial by limiting infection induced inflammation and tissue pathology. These properties make HO-1 an attractive target for host-directed therapy (HDT) of the diseases in question, many of which have been difficult to control using conventional antibiotic approaches. Here we review the mechanisms by which HO-1 expression is induced and how the enzyme regulates inflammatory and immune responses during infection with a number of different intracellular bacterial and protozoan pathogens highlighting mechanistic commonalities and differences with the goal of identifying targets for disease intervention.

Efficacy of Sulforaphane in Neurodegenerative Diseases

Sulforaphane (SFN) is a phytocompound belonging to the isothiocyanate family. Although it was also found in seeds and mature plants, SFN is mainly present in sprouts of many cruciferous vegetables, including cabbage, broccoli, cauliflower, and Brussels sprouts. SFN is produced by the conversion of glucoraphanin through the enzyme myrosinase, which leads to the formation of this isothiocyanate. SFN is especially characterized by antioxidant, anti-inflammatory, and anti-apoptotic properties, and for this reason, it aroused the interest of researchers. The aim of this review is to summarize the experimental studies present on Pubmed that report the efficacy of SFN in the treatment of neurodegenerative disease, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and multiple sclerosis (MS). Therefore, thanks to its beneficial effects, SFN could be useful as a supplement to counteracting neurodegenerative diseases.

A novel model of cerebral hyperperfusion with blood-brain barrier breakdown, white matter injury, and cognitive dysfunction

OBJECTIVE

Cerebral hyperperfusion (CHP) is associated with considerable morbidity. Its pathophysiology involves disruption of the blood-brain barrier (BBB) with subsequent events such as vasogenic brain edema and ischemic and/or hemorrhagic complications. Researchers are trying to mimic the condition of CHP; however, a proper animal model is still lacking. In this paper the authors report a novel surgically induced CHP model that mimics the reported pathophysiology of clinical CHP including BBB breakdown, white matter (WM) injury, inflammation, and cognitive impairment.

METHODS

Male Sprague-Dawley rats were subjected to unilateral common carotid artery (CCA) occlusion and contralateral CCA stenosis. Three days after the initial surgery, the stenosis of CCA was released to induce CHP. Cortical regional cerebral blood flow was measured using laser speckle flowmetry. BBB breakdown was assessed by Evans blue dye extravasation and matrix metalloproteinase-9 levels. WM injury was investigated with Luxol fast blue staining. Cognitive function was assessed using the Barnes circular maze. Other changes pertaining to inflammation were also assessed. Sham-operated animals were prepared and used as controls.

RESULTS

Cerebral blood flow was significantly raised in the cerebral cortex after CHP induction. CHP induced BBB breakdown evident by Evans blue dye extravasation, and matrix metalloproteinase-9 was identified as a possible culprit. WM degeneration was evident in the corpus callosum and corpus striatum. Immunohistochemistry revealed macrophage activation and glial cell upregulation as an inflammatory response to CHP in the striatum and cerebral cortex. CHP also caused significant impairments in spatial learning and memory compared with the sham-operated animals.

CONCLUSIONS

The authors report a novel CHP model in rats that represents the pathophysiology of CHP observed in various clinical scenarios. This model was produced without the use of pharmacological agents; therefore, it is ideal to study the pathology of CHP as well as to perform preclinical drug trials.

Virus-induced metabolic reprogramming and innate sensing hereof by the infected host

To make new infectious particles, all viruses must manipulate host cell metabolism to secure sufficient availability of biomolecules and energy-a phenomenon now known as metabolic reprogramming. Numerous observations of this has already been made for a range of viruses with each type of virus seemingly applying its own unique tactics to accomplish this unifying goal. In this light, metabolic reprogramming of the infected cell is largely beneficial to the virus and not to the host. On the other hand, virus-induced metabolic reprogramming represents a transformed self with distorted cellular and extracellular levels of distinct metabolites and metabolic by-products. This review briefly outlines current knowledge of virus-induced metabolic reprogramming, discusses how this could be sensed by the infected host to initiate anti-viral programs, and presents examples of innate anti-viral mechanisms of the host that target the availability of biomolecules to block viral replication.

CDDO-Me Distinctly Regulates Regional Specific Astroglial Responses to Status Epilepticus via ERK1/2-Nrf2, PTEN-PI3K-AKT and NFκB Signaling Pathways

2-Cyano-3,12-dioxo-oleana-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me) is a triterpenoid analogue of oleanolic acid. CDDO-Me shows anti-inflammatory and neuroprotective effects. Furthermore, CDDO-Me has antioxidant properties, since it activates nuclear factor-erythroid 2-related factor 2 (Nrf2), which is a key player of redox homeostasis. In the present study, we evaluated whether CDDO-Me affects astroglial responses to status epilepticus (SE, a prolonged seizure activity) in the rat hippocampus in order to understand the underlying mechanisms of reactive astrogliosis and astroglial apoptosis. Under physiological conditions, CDDO-Me increased Nrf2 expression in the hippocampus without altering activities (phosphorylations) of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), phosphatidylinositol-3-kinase (PI3K), and AKT. CDDO-Me did not affect seizure activity in response to pilocarpine. However, CDDO-Me ameliorated reduced astroglial Nrf2 expression in the CA1 region and the molecular layer of the dentate gyrus (ML), and attenuated reactive astrogliosis and ML astroglial apoptosis following SE. In CA1 astrocytes, CDDO-Me inhibited the PI3K/AKT pathway by activating PTEN. In contrast, CDDO-ME resulted in extracellular signal-related kinases 1/2 (ERK1/2)-mediated Nrf2 upregulation in ML astrocytes. Furthermore, CDDO-Me decreased nuclear factor-κB (NFκB) phosphorylation in both CA1 and ML astrocytes. Therefore, our findings suggest that CDDO-Me may attenuate SE-induced reactive astrogliosis and astroglial apoptosis via regulation of ERK1/2-Nrf2, PTEN-PI3K-AKT, and NFκB signaling pathways.

Dead Sea minerals: New findings on skin and the biology beyond

BACKGROUND

Therapeutic effects of Dead Sea (DS) minerals are well established, and their unique combination is analysed and reported. DS water (DSW) is a key source for DS minerals, and various studies report the capability of DSW to alleviate symptoms of different skin disorders and to contribute to skin maintenance. However, the biological mechanisms beyond reported effects are not fully understood yet.

OBJECTIVE

To elucidate the effect of topically applied DSW via the expression of different skin biomarkers related to barrier function, homeostasis, inflammation and irritation.

METHODS

In vitro skin equivalents and ex vivo human skin organ culture were used to assess the biological effects of DSW. Epidermal barrier protein expression and DSW ions transdermal penetration were analysed on skin equivalents. β-endorphin secretion was tested on human skin organ culture. The capability of DSW to protect against skin inflammation and irritation was tested on ex vivo human skin organ culture by lipopolysaccharides and sodium dodecyl sulphate addition, respectively.

RESULTS

Topical application of DSW encouraged the expression of the barrier-related proteins: filaggrin, involucrin and transglutaminase, while transdermal penetration of calcium ions was not detected. Additionally, DSW application had increased skin secretion of β-endorphin and attenuated the expression of inflammatory and irritation-related cytokines.

CONCLUSIONS

This study reports new findings of DSW effects on skin. Signalling pathway activation is proposed as a key step that may result in a vast range of proven biological activities following skin exposure to DS minerals, and specifically DSW.

The Role of the Nrf2 Signaling in Obesity and Insulin Resistance

Obesity, a metabolic disorder characterized by excessive accumulation of adipose tissue, has globally become an increasingly prevalent disease. Extensive studies have been conducted to elucidate the underlying mechanism of the development of obesity. In particular, the close association of inflammation and oxidative stress with obesity has become increasingly evident. Obesity has been shown to exhibit augmented levels of circulating proinflammatory cytokines, which have been associated with the activation of pathways linked with inflammation-induced insulin resistance, a major pathological component of obesity and several other metabolic disorders. Oxidative stress, in addition to its role in stimulating adipose differentiation, which directly triggers obesity, is considered to feed into this pathway, further aggravating insulin resistance. Nuclear factor E2 related factor 2 (Nrf2) is a basic leucine zipper transcription factor that is activated in response to inflammation and oxidative stress, and responds by increasing antioxidant transcription levels. Therefore, Nrf2 has emerged as a critical new target for combating insulin resistance and subsequently, obesity. However, the effects of Nrf2 on insulin resistance and obesity are controversial. This review focuses on the current state of research on the interplay of inflammation and oxidative stress in obesity, the role of the Nrf2 pathway in obesity and insulin resistance, and the potential use of Nrf2 activators for the treatment of insulin resistance.

Roles of NRF3 in the Hallmarks of Cancer: Proteasomal Inactivation of Tumor Suppressors

Simple Summary

This review summarizes recent advances in our understanding of the physiological roles of the NFE2-related factor 2 (NRF2)-related transcription factor NRF3 in cancer. NRF3 confers cells with six so-called “hallmarks of cancer” through upregulating gene expression of specific target genes, leading to tumorigenesis and cancer malignancy. These driver gene-like functions of NRF3 in cancer are distinct from those of NRF2.

Abstract

The physiological roles of the NRF2-related transcription factor NRF3 (NFE2L3) have remained unknown for decades. The remarkable development of human cancer genome databases has led to strong suggestions that NRF3 has functional significance in cancer; specifically, high NRF3 mRNA levels are induced in many cancer types, such as colorectal cancer and pancreatic adenocarcinoma, and are associated with poor prognosis. On the basis of this information, the involvement of NRF3 in tumorigenesis and cancer malignancy has been recently proposed. NRF3 confers cancer cells with selective growth advantages by enhancing 20S proteasome assembly through induction of the chaperone gene proteasome maturation protein (POMP) and consequently promoting degradation of the tumor suppressors p53 and retinoblastoma (Rb) in a ubiquitin-independent manner. This new finding offers insight into the proteasomal but not the genetic inactivation mechanism of tumor suppressors. Moreover, NRF3 promotes cancer malignancy-related processes, including metastasis and angiogenesis. Finally, the molecular mechanisms underlying NRF3 activation have been elucidated, and this knowledge is expected to provide many insights that are useful for the development of anticancer drugs that attenuate NRF3 transcriptional activity. Collectively, the evidence indicates that NRF3 confers cells with six so-called “hallmarks of cancer”, implying that it exhibits cancer driver gene-like function. This review describes recent research advances regarding the newly discovered addiction of cancer cells to NRF3 compared to NRF2.