The blood-brain barrier (BBB) supplies brain tissues with nutrients, filters harmful compounds from the brain back to the bloodstream, and plays a key role in iron homeostasis in the human brain. Disruptions of the BBB are associated with several neurodegenerative conditions including Parkinson's disease (PD). Oxidative stress, iron deposition and mitochondrial impaired function are considered as risk factors for degeneration of the central nervous system. Heme oxygenase (HMOX) degrades heme ring to biliverdin, free ferrous iron and carbon monoxide being the rate-limiting activity in heme catabolism. The isoform HMOX1 is highly inducible in response to reactive oxygen species, which induce an increase in BBB permeability and impair its pathophysiology. Consequently, an over- expression of this enzyme may contribute to the marked iron deposition found in PD. We analyzed the HMOX1 SNPs rs2071746, rs2071747, and rs9282702, a microsatellite (GT)n polymorphism and copy number variations in 691 patients suffering from PD and 766 healthy control individuals. Copy number variations in the HMOX1 gene exist, but these do not seem to be associated with PD risk. In contrast two polymorphisms that modify the transcriptional activity of the gene, namely a VNTR (GT)n and the SNP rs2071746, are strongly associated with PD risk, particularly with the classic PD phenotype and with early onset of the disease. This study indicates that HMOX1 gene variants are associated to the risk of developing some forms of PD, thus adding new information that supports association of HMOX gene variations with PD risk.
Parkinson's disease; Heme oxygenase; polymorphisms; copy number variations; biomarkers; blood-brain barrier; iron homeostasis
Heme oxygenase 1 (HO-1) is an essential enzyme induced by heme and multiple stimuli associated with critical illness. In humans, polymorphisms in the HMOX1 gene promoter may influence the magnitude of HO-1 expression. In many diseases including murine malaria, HO-1 induction produces protective anti-inflammatory effects, but observations from patients suggest these may be limited to a narrow range of HO-1 induction, prompting us to investigate the role of HO-1 in malaria infection. In 307 Gambian children with either severe or uncomplicated P. falciparum malaria, we characterized the associations of HMOX1 promoter polymorphisms, HMOX1 mRNA inducibility, HO-1 protein levels in leucocytes (flow cytometry), and plasma (ELISA) with disease severity. The (GT)n repeat polymorphism in the HMOX1 promoter was associated with HMOX1 mRNA expression in white blood cells in vitro, and with severe disease and death, while high HO-1 levels were associated with severe disease. Neutrophils were the main HO-1-expressing cells in peripheral blood, and HMOX1 mRNA expression was upregulated by heme-moieties of lysed erythrocytes. We provide mechanistic evidence that induction of HMOX1 expression in neutrophils potentiates the respiratory burst, and propose this may be part of the causal pathway explaining the association between short (GT)n repeats and increased disease severity in malaria and other critical illnesses. Our findings suggest a genetic predisposition to higher levels of HO-1 is associated with severe illness, and enhances the neutrophil burst leading to oxidative damage of endothelial cells. These add important information to the discussion about possible therapeutic manipulation of HO-1 in critically ill patients.
HO-1 is an important anti-inflammatory enzyme induced by several stimuli associated with critical illness. In humans, the amount of HO-1 produced is influenced by a genetic polymorphism in the gene promoter region. Using Plasmodium falciparum malaria that can cause a sepsis-like syndrome as an example, we characterize the associations between the (GT)n polymorphism, HO-1 protein levels and HMOX1-mRNA expression with severity of malaria in 307 Gambian children. Our results support the functionality of this polymorphism, demonstrate that P. falciparum infections increase HO-1 levels, and indicate that a genetic predisposition to strongly upregulate HO-1 is associated with severe forms of malaria and increased risk of dying. We identify neutrophils as the main HO-1-producing blood cells, and provide evidence that hemin-mediated induction of HMOX1 in neutrophils in vitro enhances the oxidative burst. In this way sequestered neutrophils may contribute to oxidative damage of endothelial cells, which may be part of a causal pathway explaining the association between short (GT)n repeats and increased disease severity. Our findings imply that the beneficial effects of HO-1 may be limited to a narrow window of concentrations, which should be born in mind when considering the therapeutic potential of manipulating HO-1 induction in critically ill patients.
The single nucleotide polymorphism rs2071746 and a (GT)n microsatellite within the human gene encoding heme oxygenase-1 (HMOX1) are associated with incidence or outcome in a variety of diseases. Most of these associations involve either release of heme or oxidative stress. Both polymorphisms are localized in the promoter region, but previously reported correlations with heme oxygenase-1 expression remain not coherent. This ambiguity suggests a more complex organization of the 5’ gene region which we sought to investigate more fully.
We evaluated the 5‘ end of HMOX1 and found a novel first exon 1a placing the two previously reported polymorphisms in intronic or exonic positions within the 5’ untranslated region respectively. Expression of exon 1a can be induced in HepG2 hepatoma cells by hemin and is a repressor of heme oxygenase-1 translation as shown by luciferase reporter assays. Moreover, minigene approaches revealed that the quantitative outcome of alternative splicing within the 5’ untranslated region is affected by the (GT)n microsatellite.
This data supporting an extended HMOX1 gene model and provide further insights into expression regulation of heme oxygenase-1. Alternative splicing within the HMOX1 5' untranslated region contributes to translational regulation and is a mechanistic feature involved in the interplay between genetic variations, heme oxygenase-1 expression and disease outcome.
Heme oxygenase-1 (HO-1) acts in cytoprotection against acute lung injury. The polymorphic (GT)n repeat in the HO-1 gene (HMOX1) promoter regulates HMOX1 expression. We investigated the associations of HMOX1 polymorphisms with ARDS risk and plasma HO-1 levels.
Unmatched, nested case-control study.
Academic medical center.
Consecutive patients with ARDS risk factors upon ICU admission were prospectively enrolled. Cases were 437 Caucasians who developed ARDS and controls were 1014 Caucasians who did not.
Measurements and results
We genotyped the (GT)n polymorphism and three tagging single nucleotide polymorphisms (tSNPs) in 1451 patients, and measured the plasma HO-1 levels in 106 ARDS patients. We clustered the (GT)n repeats into: S-allele (< 24 repeats), M-allele (24–30 repeats) and L-allele (≥ 31 repeats). We found that longer (GT)n repeats were associated with reduced ARDS risk (Ptrend = 0.004 for both alleles and genotypes), but no individual tSNP was associated with ARDS risk. HMOX1 haplotypes were significantly associated with ARDS risk (global test, P = 0.016), and the haplotype S-TAG was associated with increased ARDS risk (OR, 1.75; 95% CI, 1.15–2.68; P = 0.010). Intermediate-phenotype analysis showed longer (GT)n repeats were associated with higher plasma HO-1 levels (Ptrend = 0.019 for alleles and 0.027 for genotypes).
Longer (GT)n repeats in the HMOX1 promoter are associated with higher plasma HO-1 levels and reduced ARDS risk. The common haplotype S-TAG is associated with increased ARDS risk. Our results suggest that HMOX1 variation may modulate ARDS risk through the promoter microsatellite polymorphism.
acute respiratory distress syndrome; genetic susceptibility; haplotypes; heme oxygenase-1; microsatellite polymorphism; molecular epidemiology
Iron may be implicated in the generation of oxidative stress by the catalyzing the Haber–Weiss or Fenton reaction. On the other hand, oxidative stress has been implicated in the pathogenesis of age-related macular degeneration (AMD) and heme oxygenase-1 (HO-1), encoded by the HMOX1 gene and heme oxygenase-2 (HO-2), encoded by the HMOX2 gene are important markers of iron-related oxidative stress and its consequences. Therefore, variability of the HMOX1 and HMOX2 genes might be implicated in the pathogenesis of AMD through the modulation of the cellular reaction to oxidative stress. In the present work, we investigated the association between AMD and a G → C transversion at the 19 position in the HMOX1 gene (the 19G>C-HMOX1 polymorphism, rs2071747) and a A → G transition at the −42 + 1444 position in the HMOX2 gene (the −42 + 1444A>G-HMOX2 polymorphism, rs2270363) and its modulation by some environmental factors. 279 patients with AMD and 105 controls were recruited in this study and the polymorphisms were typed by restriction fragment length polymorphism and allele-specific polymerase chain reaction (PCR). We observed an association between the occurrence of dry AMD and the G/A genotype of the −42 + 1444A>G-HMOX2 polymorphism (odds ratio (OR) 2.72), whereas the G/G genotype reduced the risk of dry AMD (OR 0.41). The G/C genotype and the C allele of the 19 G>C-HMOX1 polymorphism and the G/G genotype and the G allele of the −42 + 1444A>G-HMOX2 polymorphism were associated with progression of AMD from dry to wet form (OR 4.83, 5.20, 2.55, 1.69, respectively). On the other hand, the G/G genotype and the G allele of the 19 G>C-HMOX1 polymorphism and the A/G genotype and the A allele of the −42 + 1444A>G-HMOX2 polymorphism protected against AMD progression (OR 0.19, 0.19, 0.34, 0.59, respectively). Therefore, the 19G>C-HMOX1 and the −42 + 1444A>G-HMOX2 polymorphisms may be associated with the occurrence and progression of AMD.
Electronic supplementary material
The online version of this article (doi:10.1007/s11033-011-0955-3) contains supplementary material, which is available to authorized users.
Age-related macular degeneration; AMD; Heme oxygenase-1 and -2; HMOX1, HMOX2; Gene; Polymorphism
Ozone exposure is known to cause oxidative stress. We investigated the acute effects of ozone (O3) on lung function in the elderly, a suspected risk group. We then investigated whether genetic polymorphisms of antioxidant genes (heme oxygenase-1 [HMOX1] and glutathione S-transferase pi [GSTP1]) modified these associations.
We studied 1,100 elderly men from the Normative Aging Study whose lung function (forced vital capacity [FVC] and forced expiratory volume in one second [FEV1]) was measured every 3 years from 1995–2005. We genotyped the GSTP1 Ile105Val and Ala114Val polymorphisms and the (GT)n repeat polymorphism in the HMOX1 promoter, classifying repeats as short (n<25) or long (n 25). Ambient O3 was measured continuously at locations in the Greater Boston area. We used mixed linear models, adjusting for known confounders.
A 15 ppb increase in O3 during the previous 48 hours was associated with a 1.25% decrease in FEV1 (95% CI: −1.96%, −0.54%). This estimated effect was worsened with either the presence of a long (GT)n repeat in HMOX1 (−1.38%, 95% CI: −2.11%, −0.65) or the presence of an allele coding for Val105 in GSTP1 (−1.69%, 95% CI: −2.63%, −0.75). A stronger estimated effect of O3 on FEV1 was found in subjects carrying both the GSTP1 105Val variant and the HMOX1 long (GT)n repeat (−1.94%, 95% CI: −2.89%, −0.98%). Similar associations were also found between FVC and ozone exposure.
Our results suggest that ozone has an acute effect on lung function in the elderly, and the effects may be modified by the presence of specific polymorphisms in antioxidant genes.
FEV1; FVC; GSTP1; ozone; air pollution
Heme oxygenase-1 (HMOX1) is a cytoprotective enzyme degrading heme to biliverdin, iron ions, and carbon monoxide, whose expression is induced in response to oxidative stress. Its overexpression has been suggested as a strategy improving survival of transplanted muscle precursors. Results: Here we demonstrated that HMOX1 inhibits differentiation of myoblasts and modulates miRNA processing: downregulates Lin28 and DGCR8, lowers the total pool of cellular miRNAs, and specifically blocks induction of myomirs. Genetic or pharmacological activation of HMOX1 in C2C12 cells reduces the abundance of miR-1, miR-133a, miR-133b, and miR-206, which is accompanied by augmented production of SDF-1 and miR-146a, decreased expression of MyoD, myogenin, and myosin, and disturbed formation of myotubes. Similar relationships between HMOX1 and myomirs were demonstrated in murine primary satellite cells isolated from skeletal muscles of HMOX1+/+, HMOX1+/−, and HMOX1−/− mice or in human rhabdomyosarcoma cell lines. Inhibition of myogenic development is independent of antioxidative properties of HMOX1. Instead it is mediated by CO-dependent inhibition of c/EBPδ binding to myoD promoter, can be imitated by SDF-1, and partially reversed by enforced expression of miR-133b and miR-206. Control C2C12 myoblasts injected to gastrocnemius muscles of NOD-SCID mice contribute to formation of muscle fibers. In contrast, HMOX1 overexpressing C2C12 myoblasts form fast growing, hyperplastic tumors, infiltrating the surrounding tissues, and disseminating to the lungs. Innovation: We evidenced for the first time that HMOX1 inhibits differentiation of myoblasts, affects the miRNA processing enzymes, and modulates the miRNA transcriptome. Conclusion: HMOX1 improves the survival of myoblasts, but concurrently through regulation of myomirs, may act similarly to oncogenes, increasing the risk of hyperplastic growth of myogenic precursors. Antioxid. Redox Signal. 16, 113–127.
Heme oxygenase 1 (HMOX1) is the rate limiting enzyme in heme degradation and a key regulator of inflammatory processes. In animal models the course of pancreatitis was ameliorated by up-regulation of HMOX1 expression. Additionally, carbon monoxide released during heme breakdown inhibited proliferation of pancreatic stellate cells and might thereby prevent the development of chronic pancreatitis (CP). Transcription of HMOX1 in humans is influenced by a GT-repeat located in the promoter. As such, HMOX1 variants might be of importance in the pathogenesis of pancreatitis.
The GT-repeat and SNP rs2071746 were investigated with fluorescence labelled primers and by melting curve analysis in 285 patients with acute pancreatitis, 208 patients with alcoholic CP, 207 patients with idiopathic/hereditary CP, 147 patients with alcoholic liver cirrhosis, and in 289 controls, respectively. GT-repeat analysis was extended to a total of 446 alcoholic CP patients. In addition, we performed DNA sequencing in 145 patients with alcoholic CP, 138 patients with idiopathic/hereditary CP, 147 patients with alcoholic liver cirrhosis, and 151 controls. Exon 3 screening was extended to additional patients and controls.
S- and L-alleles of the GT-repeat, genotypes and alleles of SNP rs2071746 and non-synonymous variants detected by sequencing were found with similar frequencies in all groups.
Although functional data implicate a potential influence of HMOX1 variants on the pathogenesis of pancreatitis, we did not find any association. As rare non-synonymous HMOX1 variants were found in patients and controls, it is rather unlikely that they will have functional consequences essential for pancreatitis development.
The heme oxygenase-1 gene (HMOX1) promoter polymorphisms modulate its transcription in response to oxidative stress. This study screened for HMOX1 polymorphisms and investigated the association between HMOX1 polymorphisms and coronary artery disease (CAD) in the Korean population.
The study population consisted of patients with CAD with obstructive lesions (n=110), CAD with minimal or no lesions (n=40), and controls (n=107). Thirty-nine patients with CAD with obstructive lesions underwent follow-up coronary angiography after six months for the presence of restenosis. The 5'-flanking region containing (GT)n repeats of the HMOX1 gene was analyzed by PCR.
The numbers of (GT)n repeats in the HMOX1 promoter showed a bimodal distribution. The alleles were divided into two subclasses, S25 and L25, depending on whether there were less than or equal to and more than 25 (GT)n repeats, respectively. The allele and genotype frequencies among groups were statistically not different. More subjects in the S25-carrier group had the low risk levels of high sensitivity C-reactive protein (hsCRP) for the CAD than those in the non-S25 carrier group (P=0.034). Multivariate logistic regression analysis revealed that the genotypes of (GT)n repeats were not related to CAD status. The restenosis group in the coronary angiography follow-up did not show any significant difference in HMOX1 genotype frequency.
The HMOX1 genotypes were not found to be associated with CAD, but the short allele carrier group contained more individuals with hsCRP values reflecting low risk of cardiovascular disease in the Korean population.
Coronary artery disease; Heme oxygenase-1; HMOX1 gene; Polymorphism
Rationale: Although oxidative stress is a cardinal feature of asthma, the roles of oxidant air pollutants and antioxidant genes heme oxygenase 1 (HMOX-1), catalase (CAT), and manganese superoxide dismutase (MNSOD) in asthma pathogenesis have yet to be determined.
Objectives: We hypothesized that the functional polymorphisms of HMOX-1 ([GT]n repeat), CAT (−262C>T −844C>T), and MNSOD (Ala-9Val) are associated with new-onset asthma, and the effects of these variants vary by exposure to ozone, a potent oxidant air pollutant.
Methods: We assessed this hypothesis in a population-based cohort of non-Hispanic (n = 1,125) and Hispanic white (n = 586) children who resided in 12 California communities and who were followed annually for 8 years to ascertain new-onset asthma.
Measurements and Main Results: Air pollutants were continuously measured in each of the study communities during the 8 years of study follow-up. HMOX-1 “short” alleles (<23 repeats) were associated with a reduced risk for new-onset asthma among non-Hispanic whites (hazard ratio [HR], 0.64; 95% confidence interval [CI], 0.41–0.99). This protective effect was largest in children residing in low-ozone communities (HR, 0.48; 95% CI, 0.25–0.91) (interaction P value = 0.003). Little evidence for an association with HMOX-1 was observed among Hispanic children. In contrast, Hispanic children with a variant of the CAT-262 “T” allele (CT or TT) had an increased risk for asthma (HR, 1.78; P value = 0.01). The effects of these polymorphisms were not modified by personal smoking or secondhand-smoke exposure.
Conclusions: Functional promoter variants in CAT and HMOX-1 showed ethnicity-specific associations with new-onset asthma. Oxidant gene protection was restricted to children living in low-ozone communities.
asthma; catalase; heme oxygenase-1; MnSOD; oxidative stress; ozone
Oxidative stress is generated by reactive oxygen species (ROS) produced in response to metabolic activity and environmental factors. Increased oxidative stress is associated with the pathophysiology of a broad spectrum of inflammatory diseases. Cellular response to excess ROS involves the induction of antioxidant response element (ARE) genes under control of the transcriptional activator Nrf2 and the transcriptional repressor Bach1. The development of synthetic small molecules that activate the protective anti-oxidant response network is of major therapeutic interest. Traditional small molecules targeting ARE-regulated gene activation (e.g., bardoxolone, dimethyl fumarate) function by alkylating numerous proteins including Keap1, the controlling protein of Nrf2. An alternative is to target the repressor Bach1. Bach1 has an endogenous ligand, heme, that inhibits Bach1 binding to ARE, thus allowing Nrf2-mediated gene expression including that of heme-oxygenase-1 (HMOX1), a well described target of Bach1 repression. In this report, normal human lung fibroblasts were used to screen a collection of synthetic small molecules for their ability to induce HMOX1. A class of HMOX1-inducing compounds, represented by HPP-4382, was discovered. These compounds are not reactive electrophiles, are not suppressed by N-acetyl cysteine, and do not perturb either ROS or cellular glutathione. Using RNAi, we further demonstrate that HPP-4382 induces HMOX1 in an Nrf2-dependent manner. Chromatin immunoprecipitation verified that HPP-4382 treatment of NHLF cells reciprocally coordinated a decrease in binding of Bach1 and an increase of Nrf2 binding to the HMOX1 E2 enhancer. Finally we show that HPP-4382 can inhibit Bach1 activity in a reporter assay that measures transcription driven by the human HMOX1 E2 enhancer. Our results suggest that HPP-4382 is a novel activator of the antioxidant response through the modulation of Bach1 binding to the ARE binding site of target genes.
Increases in heme oxygenase-1 (HO-1) and administration of heme degradation products CO and biliverdin inhibit vascular inflammation and vasoocclusion in mouse models of sickle cell disease (SCD). In this study, an albumin (alb) promoter-driven Sleeping Beauty (SB) transposase plasmid with a wild-type rat hmox-1 (wt-HO-1) transposable element was delivered by hydrodynamic tail vein injections to SCD mice. Eight weeks after injection, SCD mice had three- to five-fold increases in HO-1 activity and protein expression in liver, similar to hemin-treated mice. Immunohistochemistry demonstrated increased perinuclear HO-1 staining in hepatocytes. Messenger RNA transcription of the hmox-1 transgene in liver was confirmed by quantitative real-time polymerase chain reaction restriction fragment length polymorphism (qRT-PCR RFLP) with no detectible transgene expression in other organs. The livers of all HO-1 overexpressing mice had activation of nuclear phospho-p38 mitogen-activated protein kinase (MAPK) and phospho-Akt, decreased nuclear expression of nuclear factor-kappa B (NF-κB) p65, and decreased soluble vascular cell adhesion molecule-1 (sVCAM-1) in serum. Hypoxia-induced stasis, a characteristic of SCD, but not normal mice, was inhibited in dorsal skin fold chambers in wt-HO-1 SCD mice despite the absence of hmox-1 transgene expression in the skin suggesting distal effects of HO activity on the vasculature. No protective effects were seen in SCD mice injected with nonsense (ns-) rat hmox-1 that encodes carboxy-truncated HO-1 with little or no enzyme activity. We speculate that HO-1 gene delivery to the liver is beneficial in SCD mice by degrading pro-oxidative heme, releasing anti-inflammatory heme degradation products CO and biliverdin/bilirubin into circulation, activating cytoprotective pathways and inhibiting vascular stasis at sites distal to transgene expression.
Gene therapy; Heme oxygenase; Sickle cell disease; Sleeping Beauty
Oxidative stress activates the transcription factor NRF2, which in turn binds cis-acting antioxidant response element (ARE) enhancers and induces expression of protective antioxidant genes. In contrast, the transcriptional repressor BACH1 binds ARE-like enhancers in cells naïve to oxidative stress and antagonizes NRF2 binding until it becomes inactivated by pro-oxidants. Here, we describe the dynamic roles of BACH1 and NRF2 in the transcription of the heme oxygenase-1 (HMOX1) gene. HMOX1 induction, elicited by arsenite-mediated oxidative stress, follows inactivation of BACH1 and precedes activation of NRF2. BACH1 repression is dominant over NRF2-mediated HMOX1 transcription and inactivation of BACH1 is a prerequisite for HMOX1 induction. In contrast, thioredoxin reductase 1 (TXNRD1) is regulated by NRF2 but not by BACH1. By comparing the expression levels of HMOX1 with TXNRD1, we show that nuclear accumulation of NRF2 is not necessary for HMOX1 induction; rather, BACH1 inactivation permits NRF2 already present in the nucleus at low basal levels to bind the HMOX1 promoter and elicit HMOX1 induction. Thus, BACH1 confers an additional level of regulation to ARE-dependent genes that reveals a new dimension to the oxidative stress response.
Aims: Heme oxygenase-1 (HO-1, HMOX1) can prevent tumor initiation; while in various tumors, it has been demonstrated to promote growth, angiogenesis, and metastasis. Here, we investigated whether HMOX1 can modulate microRNAs (miRNAs) and regulate human non-small cell lung carcinoma (NSCLC) development. Results: Stable HMOX1 overexpression in NSCLC NCI-H292 cells up-regulated tumor-suppressive miRNAs, whereas it significantly diminished the expression of oncomirs and angiomirs. The most potently down-regulated was miR-378. HMOX1 also up-regulated p53, down-regulated angiopoietin-1 (Ang-1) and mucin-5AC (MUC5AC), reduced proliferation, migration, and diminished angiogenic potential. Carbon monoxide was a mediator of HMOX1 effects on proliferation, migration, and miR-378 expression. In contrast, stable miR-378 overexpression decreased HMOX1 and p53; while enhanced expression of MUC5AC, vascular endothelial growth factor (VEGF), interleukin-8 (IL-8), and Ang-1, and consequently increased proliferation, migration, and stimulation of endothelial cells. Adenoviral delivery of HMOX1 reversed miR-378 effect on the proliferation and migration of cancer cells. In vivo, HMOX1 overexpressing tumors were smaller, less vascularized and oxygenated, and less metastatic. Overexpression of miR-378 exerted opposite effects. Accordingly, in patients with NSCLC, HMOX1 expression was lower in metastases to lymph nodes than in primary tumors. Innovation and Conclusion:
In vitro and in vivo data indicate that the interplay between HMOX1 and miR-378 significantly modulates NSCLC progression and angiogenesis, suggesting miR-378 as a new therapeutic target. Rebound Track: This work was rejected during standard peer review and rescued by Rebound Peer Review (Antioxid Redox Signal 16, 293–296, 2012) with the following serving as open reviewers: James F. George, Mahin D. Maines, Justin C. Mason, and Yasufumi Sato. Antioxid. Redox Signal. 19, 644–660.
Preclinical toxicity of adaphostin has been related to oxidative stress. This study investigated the regulatory mechanism underlying adaphostin induction of heme oxygenase 1 (HMOX1) which plays a significant role in modulation of drug-induced toxicity in the non-small cell lung cancer cell line model, NCI-H522.
The transcriptional response of NCI-H522 to adaphostin prominently involved oxidative stress genes, particularly HMOX1. Reactive oxygen species (ROS) involvement was additionally established by generation of ROS prior to modulation of adaphostin-toxicity with antioxidants. To identify up-stream regulatory elements of HMOX1, immunofluorescence was used to evaluate nuclear translocation of the transcription factor, NF-E2-related factor 2 (Nrf2), in the presence of adaphostin. The PI3-kinase inhibitor, wortmannin, was employed as a pharmacological inhibitor of this process.
Generation of ROS provided a substantial foundation for the sensitivity of NCI-H522 to adaphostin. However, in contrast to leukemia cell lines, transcriptional response to oxidative stress was associated with induction of HMOX1, which was dependent on nuclear translocation of the transcription factor, Nrf2. Pretreatment of cells with wortmannin inhibited translocation of Nrf2 and induction of HMOX1. Wortmannin pretreatment was also able to diminish adaphostin induction of HMOX1, and as a consequence, enhance the toxicity of adaphostin to NCI-H522.
Adaphostin-induced oxidative stress in NCI-H522 was mediated through nuclear translocation of Nrf2 leading to upregulation of HMOX1. Inhibition of Nrf2 translocation by wortmannin inhibited this cytoprotective response, and enhanced the toxicity of adaphostin, suggesting that inhibitors of the PI3K pathway, such as wortmannin, might augment the antiproliferative effects of adaphostin in solid tumors that depend on the Nrf2/ARE pathway for protection against oxidative stress.
AIM: To investigate effects of iron on oxidative stress, heme oxygenase-1 (HMOX1) and hepatitis C viral (HCV) expression in human hepatoma cells stably expressing HCV proteins.
METHODS: Effects of iron on oxidative stress, HMOX1, and HCV expression were assessed in CON1 cells. Measurements included mRNA by quantitative reverse transcription-polymerase chain reaction, and protein levels by Western blots.
RESULTS: Iron, in the form of ferric nitrilotriacetate, increased oxidative stress and up-regulated HMOX1 gene expression. Iron did not affect mRNA or protein levels of Bach1, a repressor of HMOX1. Silencing the up-regulation of HMOX1 nuclear factor-erythroid 2-related factor 2 (Nrf2) by Nrf2-siRNA decreased FeNTA-mediated up-regulation of HMOX1 mRNA levels. These iron effects were completely blocked by deferoxamine (DFO). Iron also significantly decreased levels of HCV core mRNA and protein by 80%-90%, nonstructural 5A mRNA by 90% and protein by about 50% in the Con1 full length HCV replicon cells, whereas DFO increased them.
CONCLUSION: Excess iron up-regulates HMOX1 and down-regulates HCV gene expression in hepatoma cells. This probably mitigates liver injury caused by combined iron overload and HCV infection.
Deferoxamine; Core protein of hepatitis C virus; Hepatitis C; Iron; Heme oxygenase-1; Nuclear factor-erythroid 2-related factor 2; Bach1; Oxidative stress; Nonstructural 5A protein of hepatitis C virus
placental vasculature is critical for nutrient, gas, and waste exchange between the maternal and fetal systems. Its development depends on the proper expression and interaction of angiogenesis and associated growth factors. Heme oxygenase (HMOX), the enzyme for heme degradation, plays a role in angiogenesis and is highly expressed in the placenta. To evaluate the role of maternal HMOX1, the inducible HMOX isozyme, on placental vasculature formation, mice with a partial deficiency in Hmox1 (Hmox1+/−) were used. Three-dimensional images of placental vasculatures as well as spiral arteries from Hmox1+/+ or Hmox1+/− placentas were created by vascular corrosion casting technique and imaged by micro-computerized tomography (microCT).
The structures and morphologies of fetomaternal interfaces were observed by histological staining and the ultrastructure of uterine natural killer (uNK) cells, a major regulator in spiral artery remodeling, was analyzed by transmission electron microscopy. A group of growth factors and angiogenic factors from the decidua/mesometrial lymphoid aggregate of pregnancy (MLAp) as well as labyrinth regions were quantified using an angiogenesis PCR array kit and compared between Hmox1+/+ or Hmox1+/− placentas. In conclusion, a partial deficiency of maternal Hmox1 resulted in the malformation of fetomaternal interface, insufficiency of spiral artery remodeling, and alteration of uNK cell differentiation and maturation. These changes were independent of the fetal genotype, but relied on the maternal HMOX1 level, which determined the balance of expression levels of pro- and antiangiogenic factors in the decidua/MLAp region. These results implied that Hmox1 polymorphisms among the human population might contribute to some unexplained cases of pregnancy disorders, such as fetal growth retardation and preeclampsia.
Maternal HMOX1 is essential for the formation of the fetomaternal interface, remodeling of the uterine spiral arteries, and differentiation and maturation of uNK cells; its effects are primarily mediated through the regulation of a group of pro- and anti-angiogenesis factors in the decidua/MLAp region.
angiogenesis; heme oxygenase 1; intrauterine growth restriction (IUGR); placenta; spiral artery remodeling; uterine natural killer (uNK) cell
Red meat is a risk factor for colorectal cancer (CRC). We wanted to evaluate whether a functional polymorphism in the HMOX1 gene encoding heme oxygenase modifies risk of CRC or interacts with diet or lifestyle factors because this would identify heme or heme iron as a risk factor of CRC. The HMOX1 A-413T (rs2071746) was assessed in relation to risk of colorectal cancer (CRC) and interactions with diet (red meat, fish, fiber, cereals, fruit and vegetables) and lifestyle (use of non-steroidal anti-inflammatory drug and smoking status) were assessed in a case-cohort study of 928 CRC cases and a comparison group of 1726 randomly selected participants from a prospective study of 57,053 persons. No association between HMOX1 A-413T and CRC risk was found (TT vs. AA + TA; IRR = 1.15, 95% CI: 0.98–1.36, p = 0.10 for the adjusted estimate). No interactions were found between diet or lifestyle and HMOX1 A-413T. HMOX1 A-413T was not associated with CRC risk and no interactions with diet or lifestyle were identified in this large, prospective cohort with high meat intake. The results reproduced the previous findings from the same cohort and did not support a link between heme or heme iron and colorectal cancer. These results should be sought and replicated in other well-characterized cohorts with high meat intake.
genetic epidemiology; colorectal cancer; heme iron; heme; meat intake; heme oxygenase; polymorphism; gene-environment interaction
Background and Aims
Hepatitis C virus (HCV) infection is associated with systemic oxidative stress. Since the heme catabolic pathway plays an important role in antioxidant protection, we attempted to assess the gene expression of key enzymes of heme catabolism, heme oxygenase 1 (HMOX1), heme oxygenase 2 (HMOX2), and biliverdin reductase A (BLVRA) in the liver and peripheral blood leukocytes (PBL) of patients chronically infected with HCV.
Gene expressions (HMOX1, HMOX2, BLVRA) and HCV RNA were analyzed in PBL of HCV treatment naïve patients (n = 58) and controls (n = 55), with a subset of HCV patients having data on hepatic gene expression (n = 35). Based upon the therapeutic outcome, HCV patients were classified as either responders (n = 38) or treatment-failure patients (n = 20). Blood samples in HCV patients were collected at day 0, and week 12, 24, 36, and 48 after the initiation of standard antiviral therapy.
Compared to the controls, substantially increased BLVRA expression was detected in PBL (p<0.001) of therapeutically naïve HCV patients. mRNA levels of BLVRA in PBL closely correlated with those in liver tissue (r2 = 0.347,p = 0.03). A marked difference in BLVRA expression in PBL between the sustained responders and patients with treatment failure was detected at week 0 and during the follow-up (p<0.001). Multivariate analysis revealed that BLVRA basal expression in PBL was an independent predictor for sustained virological response (OR 15; 95% CI 1.05–214.2; P = 0.046). HMOX1/2 expression did not have any effect on the treatment outcome.
Our results suggest that patients with chronic HCV infection significantly upregulate BLVRA expression in PBL. The lack of BLVRA overexpression is associated with non-responsiveness to standard antiviral therapy; whereas, HMOX1/2 does not seem to have any predictive potential.
Heme oxygenases (HO) catalyze the rate-limiting step of heme degradation. The cytoprotective action of the inducible HO-1 isoform, encoded by the Hmox1 gene, is required for host protection against systemic infections. Here we report that upregulation of HO-1 expression in macrophages (Mϕ) is strictly required for protection against mycobacterial infection in mice. HO-1-deficient (Hmox1−/−) mice are more susceptible to intravenous Mycobacterium avium infection, failing to mount a protective granulomatous response and developing higher pathogen loads, than infected wild-type (Hmox1+/+) controls. Furthermore, Hmox1−/− mice also develop higher pathogen loads and ultimately succumb when challenged with a low-dose aerosol infection with Mycobacterium tuberculosis. The protective effect of HO-1 acts independently of adaptive immunity, as revealed in M. avium-infected Hmox1−/− versus Hmox1+/+ SCID mice lacking mature B and T cells. In the absence of HO-1, heme accumulation acts as a cytotoxic pro-oxidant in infected Mϕ, an effect mimicked by exogenous heme administration to M. avium-infected wild-type Mϕ in vitro or to mice in vivo. In conclusion, HO-1 prevents the cytotoxic effect of heme in Mϕ, contributing critically to host resistance to Mycobacterium infection.
Glutathione S-transferase (GST) and heme oxygenase-1 (HMOX1) genes encode enzymes that detoxify carcinogens and protect against oxidative stress. We studied gene-smoking interactions on rheumatoid arthritis (RA) susceptibility.
549 matched Caucasian RA cases and controls were selected from the Nurses' Health Study. Genotyping by TaqMan and BioTrove identified GSTM1, GSTT1 homozygous deletions (null) and GSTP1 (rs1695), HMOX1 (rs2071746) alleles, respectively. We studied gene-smoking interactions on the risk of all RA and serologic RA phenotypes in separate logistic models adjusted for covariates. We assessed multiplicative interactions with product terms in the logistic models and additive interactions with the attributable proportion due to interaction (AP). For replication, we repeated significant analyses in an independent case-control sample from the Epidemiologic Investigation of RA.
For all RA risk, we observed: multiplicative (p=0.05) and additive (AP=0.53, p=0.0005) interactions between GSTT1-null and smoking and multiplicative interaction (p=0.05) between HMOX1 and smoking. For seropositive RA risk, we found multiplicative (p=0.01) and additive (AP=0.63, p<0.0001) interactions between GSTT1-null and smoking and additive interaction (AP=0.41, p=0.03) between HMOX1 and smoking. After correction for multiple comparisons, additive interactions for GSTT1-null and smoking remained significant. GSTM1-null and GSTP1 did not show significant interactions. No associations were seen with seronegative RA. In replication analyses, we observed significant multiplicative (p=0.04) and additive (AP=0.32, p=0.02) interactions between GSTT1-null and smoking for ACPA-positive RA risk.
We observed significant gene-environment interactions between GSTT1-null and heavy smoking on RA risk. Future studies are needed to assess the impact of these interactions on RA prediction.
The let-7 microRNA (miRNA) plays important roles in human liver development and disease such as hepatocellular carcinoma, liver fibrosis and hepatitis wherein oxidative stress accelerates the progression of these diseases. To date, the role of the let-7 miRNA family in modulation of heme oxygenase 1 (HMOX1), a key cytoprotective enzyme, remains unknown. Our aims were to determine whether let-7 miRNA directly regulates Bach1, a transcriptional repressor of the HMOX1 gene, and whether indirect up-regulation of HMOX1 by let-7 miRNA attenuates oxidant injury in human hepatocytes. The effects of let-7 miRNA on Bach1 and HMOX1 gene expression in Huh-7 and HepG2 cells were determined by real-time qRT-PCR, Western blot, and luciferase reporter assays. Dual luciferase reporter assays revealed that let-7b, let-7c, or miR-98 significantly decreased Bach1 3’-untranslated region (3’-UTR)-dependent luciferase activity but not mutant Bach1 3’-UTR-dependent luciferase activity, whereas mutant let-7 miRNA containing base complementarity with mutant Bach1 3’-UTR restored its effect on mutant reporter activity. let-7b, let-7c, or miR-98 down-regulated Bach1 protein levels by 50–70%, and subsequently up-regulated HMOX1 gene expression by 3–4 fold, compared with non-specific controls. Furthermore, Huh-7 cells transfected with let-7b, let-7c or miR-98 mimic showed increased resistance against oxidant injury induced by tert-butyl-hydroperoxide (tBuOOH), whereas the protection was abrogated by over-expression of Bach1. In conclusion, let-7 miRNA directly acts on the 3’-UTR of Bach1 and negatively regulates expression of this protein, and thereby up-regulates HMOX1 gene expression. Over-expression of the let-7 miRNA family members may represent a novel approach to protecting human hepatocytes from oxidant injury.
let-7; HMOX1; Bach1; microRNA; oxidative stress; Huh-7 cell
Hepatitis C virus (HCV) directly induces oxidative stress and liver injury. Bach1, a zipper (bZip) mammalian transcriptional repressor, negatively regulates heme oxygenase 1 (HMOX1), a key cytoprotective enzyme that has anti-oxidant and anti-inflammatory activities. microRNAs are small non-coding RNAs (~22 nt) that are important regulators of gene expression. Whether and how microRNAs regulate Bach1 or HCV are largely unknown. The aims of this study were to determine whether miR-196 regulates Bach1, HMOX1, and/or HCV gene expression. HCV replicon cell lines (Con1 and 9-13) of the Con1 isolate and J6/JFH1-based HCV cell culture system were used in this study. The effects of miR-196 mimic on Bach1, HMOX1 and HCV RNA and protein levels were measured by qRT-PCR and Western blots, respectively. The Dual Glo™ Luciferase Assay System was used to determine reporter activities. miR-196 mimic significantly down-regulated Bach1 and up-regulated HMOX1 gene expression, and inhibited HCV expression. Dual luciferase reporter assays demonstrated that transfection of miR-196 mimic resulted in a significant decrease in Bach1 3′-UTR-dependent luciferase activity but not in mutant Bach1 3′-UTR-dependent luciferase activity. Moreover, there was no detectable effect of mutant miR-196 on Bach1 3′-UTR-dependent luciferase activity.
miR-196 directly acts on the 3′-UTR of Bach1 mRNA and translationally represses the expression of this protein, and up-regulates HMOX1. miR-196 also inhibits HCV expression in HCV replicon cell lines (genotype 1b) and in J6/JFH1 (genotype 2a) HCV cell culture system. Thus, miR-196 plays a role in both HMOX1/Bach1 expression and the regulation of HCV expression in human hepatocytes. Over-expression of miR-196 holds promise as a potential novel strategy to prevent or ameliorate hepatitis C infection, and to protect against liver injury in chronic HCV infection.
microRNA; heme oxygenase-1; hepatitis C virus; 3′-UTR; reporter gene assay
Background and objectives
We have previously shown that reduced defenses against oxidative stress due to glutathione S-transferase M1 (GSTM1) deletion modify the effects of PM2.5 (fine-particulate air pollution of < 2.5 μm in aerodynamic diameter) on heart rate variability (HRV) in a cross-sectional analysis of the Normative Aging Study, an elderly cohort. We have extended this to include a longitudinal analysis with more subjects and examination of the GT short tandem repeat polymorphism in the heme oxygenase-1 (HMOX-1) promoter.
HRV measurements were taken on 539 subjects. Linear mixed effects models were fit for the logarithm of HRV metrics—including standard deviation of normal-to-normal intervals (SDNN), high frequency (HF), and low frequency (LF)—and PM2.5 concentrations in the 48 hr preceding HRV measurement, controlling for confounders and a random subject effect.
PM2.5 was significantly associated with SDNN (p = 0.04) and HF (p = 0.03) in all subjects. There was no association in subjects with GSTM1, whereas there was a significant association with SDNN, HF, and LF in subjects with the deletion. Similarly, there was no association with any HRV measure in subjects with the short repeat variant of HMOX-1, and significant associations in subjects with any long repeat. We found a significant three-way interaction of PM2.5 with GSTM1 and HMOX-1 determining SDNN (p = 0.008), HF (p = 0.01) and LF (p = 0.04). In subjects with the GSTM1 deletion and the HMOX-1 long repeat, SDNN decreased by 13% [95% confidence interval (CI), −21% to −4%], HF decreased by 28% (95% CI, −43% to −9%), and LF decreased by 20% (95% CI, −35% to −3%) per 10 μg/m3 increase in PM.
Oxidative stress is an important pathway for the autonomic effects of particles.
air particles; air pollution; cardiovascular health; genetic variation; GST; heart rate variability; HMOX-1; PM2.5
Case-control studies have successfully identified many significant genetic associations for complex diseases, but lack of replication has been a criticism of case-control genetic association studies in general. We selected 12 candidate genes with reported associations to chronic obstructive pulmonary disease (COPD) and genotyped 29 polymorphisms in a family-based study and in a case-control study. In the Boston Early-Onset COPD Study families, significant associations with quantitative and/or qualitative COPD-related phenotypes were found for the tumor necrosis factor (TNF)-α −308G>A promoter polymorphism (P < 0.02), a coding variant in surfactant protein B (SFTPB Thr131Ile) (P = 0.03), and the (GT)31 allele of the heme oxygenase (HMOX1) promoter short tandem repeat (P = 0.02). In the case-control study, the SFTPB Thr131Ile polymorphism was associated with COPD, but only in the presence of a gene-by-environment interaction term (P = 0.01 for both main effect and interaction). The 30-repeat, but not the 31-repeat, allele of HMOX1 was associated (P = 0.04). The TNF −308G>A polymorphism was not significant. In addition, the microsomal epoxide hydrolase “fast” allele (EPHX1 His139Arg) was significantly associated in the case-control study (P = 0.03). Although some evidence for replication was found for SFTPB and HMOX1, none of the previously published COPD genetic associations was convincingly replicated across both study designs.
association studies; case-control studies; emphysema; genetics; single nucleotide polymorphism