Genetic Variations and Haplotype Structures of Transcriptional Pactor Nrf2 and Its Cytosolic Reservoir Protein Keap1 in Japanese

Research for type 2 diabetes mellitus in endemic arsenism areas in central China: role of low level of arsenic exposure and KEAP1 rs11545829 polymorphism

Type 2 diabetes mellitus (T2DM) is one of the major public health problems worldwide; both genetic and environmental factors are its risk factors. Arsenic, an environmental pollutant, might be a risk factor for T2DM, but the association of low-to-moderate level arsenic exposure with the risk of T2DM is still inconsistent. Single nucleotide polymorphisms (SNPs) can affect the development of T2DM, but the study on KEAP1 rs11545829 (G>A) SNP is few. In this paper, we explored the effect of KEAP1 rs11545829 (G>A) SNP and low-to-moderate level arsenic exposure on risk of T2DM in a cross-sectional case-control study conducted in Shanxi, China. Total of 938 participants, including 318 T2DM cases and 618 controls, were enrolled. Blood glycosylated haemoglobin (HbA1c) was detected by Automatic Biochemical Analyzer, and participants with HbA1c≧6.5% were diagnosed as T2DM. Urinary total arsenic (tAs, mg/L), as the indicator of arsenic exposure, was detected by liquid chromatography-atomic fluorescence spectrometry (LC-AFS). Genomic DNA was extracted and the genotypes of KEAP1 rs11545829 SNP were examined by multiplex polymerase chain reaction (PCR). The urinary tAs concentration in recruited participants was 0.075 (0.03-0.15) mg/L, and was associated with an increased risk of T2DM (OR = 8.45, 95% CI 2.63-27.17); rs11545829 mutation homozygote AA genotype had a protective effect on risk of T2DM (OR = 0.42, 95 % CI 0.25-0.73). Although this protective effect of AA genotype was found in participants with higher urinary tAs level (>0.032 mg/L) (OR = 0.48, 95% CI 0.26-0.86), there was no interaction effect for arsenic exposure and rs11545829 SNP on risk of T2DM. In addition, BMI modified the association between rs11545829 SNP and the risk of T2DM (RERI = -1.11, 95% CI -2.18-0.04). The present study suggest that low-to-moderate level arsenic exposure may be a risk factor, while KEAP1 rs11545829 SNP mutation homozygote AA genotype may be a protective factor for risk of T2DM, especially for T2DM patients with urinary tAs level>0.032 mg/L.

AHR and NRF2 in Skin Homeostasis and Atopic Dermatitis

Skin is constantly exposed to environmental insults, including toxic chemicals and oxidative stress. These insults often provoke perturbation of epidermal homeostasis and lead to characteristic skin diseases. AHR (aryl hydrocarbon receptor) and NRF2 (nuclear factor erythroid 2-related factor 2) are transcription factors that induce a battery of cytoprotective genes encoding detoxication and antioxidant enzymes in response to environmental insults. In addition to their basic functions as key regulators of xenobiotic and oxidant detoxification, recent investigations revealed that AHR and NRF2 also play critical roles in the maintenance of skin homeostasis. In fact, specific disruption of AHR function in the skin has been found to be associated with the pathogenesis of various skin diseases, most prevalently atopic dermatitis (AD). In this review, current knowledge on the roles that AHR and NRF2 play in epidermal homeostasis was summarized. Functional annotations of genetic variants, both regulatory and nonsynonymous SNPs, identified in the AHR and NRF2 loci in the human genome were also summarized. Finally, the possibility that AHR and NRF2 serve as therapeutic targets of AD was assessed.

Efficacy of short-term intensive treatment with insulin pump to improve islet β-cell function in newly diagnosed type 2 diabetes via inhibition of oxidative stress

The present study (Chinese Trial Registry GTB7027) assessed the effects of short-term intensive treatment with insulin pump on islet cell function in patients with newly diagnosed type 2 diabetes and the possible mechanism. A total of 100 patients newly diagnosed with type 2 diabetes and hospitalized between January 2016 and December 2017 were divided into a control and an experimental group (n=50 in each group). The subjects of the control group were administered multiple insulin injections for intensive treatment, while the experimental group received short-term intensive treatment with an insulin pump. Analysis of blood parameters, including lipids and glucose, as well as islet β-cell function were performed. The level of reactive oxygen species (ROS) in the peripheral blood mononuclear cells (PBMCs) from the patients was also measured. Oxidative stress indicators, including serum malondialdehyde (MDA) and superoxide dismutase (SOD), were also examined to explore the possible mechanism. The mRNA expression of heme oxygenase 1 (HO-1) and nuclear factor erythroid 2-related factor 2 (Nrf2) in PBMCs were analyzed by reverse transcription-quantitative PCR. The results indicated that the blood lipid levels were significantly improved in the two groups at two weeks, while the experimental group had significantly lower levels of total cholesterol and triglyceride, as well as low- and high-density lipoprotein cholesterol. The function of islet β-cells was significantly improved in the two groups. The insulin secretion index [homeostasis model assessment (HOMA) of β-cell function] in the experimental group was higher, while the insulin resistance (IR) index (HOMA of IR) was significantly lower than that in the control group. The serum MDA level in the experimental group was significantly lower and the SOD level was significantly higher compared with that in the control group. Following treatment, the level of ROS in diabetic PBMCs was significantly reduced, and the transcription level of HO-1 and Nrf2 were also significantly reduced (P<0.05). These results demonstrated that short-term intensive treatment with an insulin pump significantly improved lipid and blood glucose metabolism to protect islet function as well as significantly reducing the level of oxidative stress in patients with newly diagnosed type 2 diabetes.

Rare and common genetic variations in the Keap1/Nrf2 antioxidant response pathway impact thyroglobulin gene expression and circulating levels, respectively

Nuclear factor, erythroid 2-like 2 (Nrf2) is a transcription factor that has been gaining attention in the field of pharmacology and especially in the chemoprevention of diseases such as cancer, metabolic and neurodegenerative diseases, etc. This is because natural compounds such as sulforaphane, which is found in broccoli sprout extracts, can activate Nrf2. The repertoire of the roles of Nrf2 is ever increasing; besides its traditional antioxidant and cytoprotective effects, Nrf2 can have other functions as a transcription factor. We have recently shown that Nrf2 directly regulates the expression of thyroglobulin (Tg), which is the most abundant thyroidal protein and the precursor of thyroid hormones. Two functional binding sites for Nrf2 (antioxidant response elements, AREs) were identified in the regulatory region of the TG gene. Interestingly, we then observed that one of these AREs harbors a rare single-nucleotide polymorphism (SNP). Also recently, we performed the first genome-wide association study (GWAS) for common SNPs that impact the circulating levels of Tg. Based on these investigations, we were triggered (i) to investigate whether common SNPs in the Nrf2 pathway correlate with circulating Tg levels; and (ii) to examine whether the rare SNP in one of the TG regulatory AREs may affect gene expression. To address the first question, we analyzed GWAS data from a general population and its two subpopulations, one with thyroid disease and/or abnormal thyroid function tests and the other without, in which circulating Tg levels had been measured. Statistically significant associations with Tg levels were observed in the genes encoding Nrf2 and Keap1, including, notably, a known functional SNP in the promoter of the gene encoding Nrf2. Regarding the rare SNP (rs778940395) in the proximal ARE of the TG enhancer, luciferase reporter gene expression studies in PCCL3 rat thyroid follicular cells showed that this SNP abrogated the basal and sulforaphane- or TSH-induced luciferase activity, behaving as a complete loss-of-function mutation. Thus, both rare and common genetic variation in the Keap1/Nrf2 pathway can impact TG expression and Tg circulating levels, respectively.

Functional polymorphisms in Nrf2: implications for human disease

Nuclear factor (erythroid derived)-2 like 2 (NFE2L2), also known as nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2), is a ubiquitous transcription factor essential for protecting cells and tissues from oxidative stress-induced injury. Positional cloning and studies with Nrf2 knockout mice have identified important roles for this transcription factor in disease phenotypes for many organ systems. Studies have also characterized the means through which human Nrf2 is regulated and the mechanisms of interaction with antioxidant response elements (ARE) in promoters of effector genes. Moreover, single nucleotide polymorphisms (SNPs) in Nrf2 have been identified and evaluated for effects on gene expression and function, and translational investigations have sought to determine whether loss of function SNPs associate with disease progression. In this review, we present 1) an overview of the human Nrf2 gene and protein domain, 2) identification of genetic mutations in Nrf2 and associations of the mutations with multiple diseases, and 3) the role of somatic mutations in Nrf2 in diseases, primarily various cancers.

Association of Nrf2 polymorphism haplotypes with acute lung injury phenotypes in inbred strains of mice

AIMS

Nrf2 is a master transcription factor for antioxidant response element (ARE)-mediated cytoprotective gene induction. A protective role for pulmonary Nrf2 was determined in model oxidative disorders, including hyperoxia-induced acute lung injury (ALI). To obtain additional insights into the function and genetic regulation of Nrf2, we assessed functional single nucleotide polymorphisms (SNPs) of Nrf2 in inbred mouse strains and tested whether sequence variation is associated with hyperoxia susceptibility.

RESULTS

Nrf2 SNPs were compiled from publicly available databases and by re-sequencing DNA from inbred strains. Hierarchical clustering of Nrf2 SNPs categorized the strains into three major haplotypes. Hyperoxia susceptibility was greater in haplotypes 2 and 3 strains than in haplotype 1 strains. A promoter SNP -103 T/C adding an Sp1 binding site in haplotype 2 diminished promoter activation basally and under hyperoxia. Haplotype 3 mice bearing nonsynonymous coding SNPs located in (1862 A/T, His543Gln) and adjacent to (1417 T/C, Thr395Ile) the Neh1 domain showed suppressed nuclear transactivation of pulmonary Nrf2 relative to other strains, and overexpression of haplotype 3 Nrf2 showed lower ARE responsiveness than overexpression of haplotype 1 Nrf2 in airway cells. Importantly, we found a significant correlation of Nrf2 haplotypes and hyperoxic lung injury phenotypes.

INNOVATION AND CONCLUSION

The results indicate significant influence of Nrf2 polymorphisms and haplotypes on gene function and hyperoxia susceptibility. Our findings further support Nrf2 as a genetic determinant in ALI pathogenesis and provide useful tools for investigators who use mouse strains classified by Nrf2 haplotypes to elucidate the role for Nrf2 in oxidative disorders.

Nuclear factor erythroid 2-related factor gene variants and susceptibility of arsenic-related skin lesions

Inorganic arsenic (iAs) is an important pollutant associated with various chronic-degenerative diseases. The cytoprotective protein nuclear factor erythroid 2-related factor (NRF2) has been proposed as an important responsive mechanism against iAs exposure. The aim of this study was to determine whether the risk of skin lesions in people exposed to iAs-contaminated water could be modified by the presence of single nucleotide polymorphisms in the NRF2 coding gene. We studied 117 individuals with long-term iAs exposure and 120 nonexposed individuals. Total As was determined in water, meanwhile iAs and its metabolites were measured in urine. The iAs-induced skin lesion status was evaluated by expert dermatologists. We sequenced the promoter region of NRF2 in a sample of 120 healthy donors. We found four polymorphisms previously reported and one novel polymorphism in the 5′ regulatory region of the NRF2. In this study, we did not find allelic and genotype association of NRF2 polymorphisms with iAs-related skin lesion. However, the analysis of haplotypes composed by –653GA, and –617CA NRF2 single nucleotide polymorphisms showed a significant association with protection against skin lesions in the low-As exposure group. This is the first report studying the association between NRF2 polymorphisms and susceptibility of As-related skin lesions. Increasing the sample size will allow us to confirm this data.

Genomic structure and variation of nuclear factor (erythroid-derived 2)-like 2

High-density mapping of mammalian genomes has enabled a wide range of genetic investigations including the mapping of polygenic traits, determination of quantitative trait loci, and phylogenetic comparison. Genome sequencing analysis of inbred mouse strains has identified high-density single nucleotide polymorphisms (SNPs) for investigation of complex traits, which has become a useful tool for biomedical research of human disease to alleviate ethical and practical problems of experimentation in humans. Nuclear factor (erythroid-derived 2)-like 2 (NRF2) encodes a key host defense transcription factor. This review describes genetic characteristics of human NRF2 and its homologs in other vertebrate species. NRF2 is evolutionally conserved and shares sequence homology among species. Compilation of publically available SNPs and other genetic mutations shows that human NRF2 is highly polymorphic with a mutagenic frequency of 1 per every 72 bp. Functional at-risk alleles and haplotypes have been demonstrated in various human disorders. In addition, other pathogenic alterations including somatic mutations and misregulated epigenetic processes in NRF2 have led to oncogenic cell survival. Comprehensive information from the current review addresses association of NRF2 variation and disease phenotypes and supports the new insights into therapeutic strategies.

Effect of NFE2L2 genetic polymorphism on the association between oral estrogen therapy and the risk of venous thromboembolism in postmenopausal women

Oral, but not transdermal, estrogen therapy increases the risk of venous thromboembolism (VTE) in women who are past menopause. Data from the Estrogen and Thromboembolism Risk (ESTHER) study were used to investigate the effects of the genetic polymorphism of NFE2L2 rs6721961, which may impair Nrf2-dependent hepatic conjugation of estrogen metabolites. As compared with nonusers, the odds ratio (OR) for VTE in current users of oral estrogens was 2.5 (95% confidence interval (CI): 1.3-4.8) in patients with wild-type NFE2L2 and 17.9 (95% CI: 3.7-85.7) in those with the polymorphism (interaction, P = 0.01).

The NRF2 gene variant, -653G/A, is associated with nephritis in childhood-onset systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease associated with oxidative stress and characterized by chronic inflammation. Kidney malfunction, an aggressive characteristic of this disease, is not present in all affected individuals. The Nrf2-Keap1 pathway is important in protecting against oxidative stress and inflammation. Mouse models and genome-wide scans have suggested NRF2 (Nuclear factor (erythroid-derived 2)-like 2) as a candidate gene for susceptibility to SLE. We therefore investigated whether NRF2 polymorphisms are associated with childhood-onset SLE in a Mexican Mestizo population. Two single nucleotide polymorphisms (SNPs) were genotyped by TaqMan((R)) assays in 362 patients with childhood-onset SLE and 379 controls. We found no significant association between susceptibility to SLE and NRF2 polymorphisms. However, after population stratification by gender, the heterozygous genotype of the -653G/A SNP was significantly associated with nephritis in females only [OR = 1.81, CI (1.04-3.12), p = 0.032]. This association was stronger in females affected with severe nephritis [classes IV-VI; OR = 2.16, CI (1.12-4.15), p = 0.019]. Our results suggest that NRF2 is not associated with susceptibility to childhood-onset SLE, but it could confer a risk for developing kidney malfunction in SLE-affected individuals.

The keap1-nrf2 cellular defense pathway: mechanisms of regulation and role in protection against drug-induced toxicity

Adverse drug reactions pose a significant public health problem. In some cases, the process of drug metabolism can contribute to the onset of toxicity through the bioactivation of a parent molecule to a chemically reactive intermediate. In order to maintain a favorable balance between bioactivation and detoxification, mammalian cells have evolved an inducible cell defense system known as the antioxidant response pathway. The activity of this cytoprotective pathway is largely regulated by the transcription factor Nrf2, which governs the expression of many phase II detoxification and antioxidant enzymes. In turn, the activity of Nrf2 is regulated by the cysteine-rich cytosolic inhibitor Keap1, which acts as a "sensor" for chemical/oxidative stress. This article summarizes our current understanding of the molecular mechanisms that regulate the function of the Keap1-Nrf2 pathway and highlights the importance of Nrf2 in the protection against drug-induced toxicity.

The hepatotoxic metabolite of acetaminophen directly activates the Keap1-Nrf2 cell defense system

The transcription factor Nrf2 regulates the expression of numerous cytoprotective genes in mammalian cells. We have demonstrated previously that acetaminophen activates Nrf2 in mouse liver following administration of non-hepatotoxic and hepatotoxic doses in vivo, implying that Nrf2 may have an important role in the protection against drug-induced liver injury. Nrf2 activation has been proposed to occur through the modification of cysteine residues within Keap1, the cytosolic repressor of Nrf2. We hypothesized that acetaminophen activates Nrf2 via the formation of its reactive metabolite N-acetyl-p-benzoquinoneimine (NAPQI), which may disrupt the repression of Nrf2 through the modification of cysteine residues within Keap1. Here, we show that NAPQI can directly activate the Nrf2 pathway in mouse liver cells, inducing an adaptive defense response that is antagonized by RNA interference targeted against Nrf2. Furthermore, mass spectrometric analysis shows that NAPQI selectively modifies cysteine residues in Keap1, both in recombinant protein in vitro and in cells ectopically expressing Keap1. Using this cell-based model, we demonstrate that activation of Nrf2 by NAPQI and a panel of probe molecules [dexamethasone 21-mesylate, 15-deoxy-Delta-((12,14))-prostaglandin J(2), 2,4-dinitrochlorobenzene, and iodoacetamide] correlates with the selective modification of cysteine residues located within the intervening region of Keap1. However, substantial depletion of glutathione (to less than 15% of basal levels) by buthionine sulfoximine, which does not directly modify Keap1, is also sufficient to activate Nrf2.

CONCLUSION

Nrf2 can be activated via the direct modification of cysteine residues located within the intervening region of Keap1, but also via the substantial depletion of glutathione without the requirement for direct modification of Keap1. It is possible that both of these mechanisms contribute to the activation of Nrf2 by acetaminophen.