Oxidative stress, thiol redox signaling methods in epigenetics

Crotonaldehyde induced structural alterations in Low-Density Lipoprotein: Immunogenicity of the modified protein in experimental animals and auto-antibodies generation in various cancers

Crotonaldehyde (CA), a prominent component of cigarette smoke (CS) is a pervasive environmental pollutant that is a highly toxic, unsaturated aldehyde. Exposure to CA-rich pollutants has been linked to the emergence of many malignancies in humans. To better understand the role of CA in biomolecule modification, this study investigated the detailed structural alterations in low-density lipoprotein (LDL) modified by CA, as well as the immunogenicity of the modified protein in experimental animals and the search for autoantibodies in various cancers patients.In vitro, results indicated alterations in secondary and tertiary structures; examined using UV-visible, fluorescence, far-UV circular dichroism, and Fourier transform infrared spectroscopy techniques. Changes in the oxidation status of LDL were studied by carbonyl content assay and NBT assay. ThT binding assay, scanning, and transmission electron microscopy were used to study aggregate formation. The findings revealed significant structural damage in LDL modified by CA. The modification resulted in the unmasking of hydrophobic clusters, the loss of the protein α-helix, and the formation of β-pleated sheet structure. The amyloid aggregate formation was confirmed through ThT microscopy and electron spectroscopy. Rabbits immunized with crotonaldehyde; lead to structural changes in the LDL; that acted as extra antigenic determinants, eliciting strong antibody response. Immunoglobulin response is highly specific for modified LDL as demonstrated by the ELISA. The presence of antibodies against CA-modified LDL was confirmed by the immunoglobulin content of blood sera from human subjects with lung cancer, and competitive ELISA demonstrated the specificity of these antibodies. This study offers insights into the CA-mediated LDL modification and immunogenicity in lung cancer that will have diagnostic importance.

Potential Role of Epigenetics and Redox Signaling in the Gut-Brain Communication and the Case of Autism Spectrum Disorder

The gut-brain axis refers to the bidirectional connection and communication between the gastrointestinal tract and the central nervous system. This paper explores two routes for this communication that have hitherto remained under-examined: epigenetics and redox signaling and their implications for autism spectrum disorder (ASD). The gut microbiota may induce epigenetic changes in the gut and potentially in the brain through their fermentation products. Instead of through other conceptualizations of them acting as neurotransmitters, gut microbial products may act as epigenetic agents, which are supported by the effects of gut bacterial-derived metabolites on gene regulation and expression. In addition to their epigenetic effects, gut bacterial-derived communicative agents can also influence host signaling by contributing to and even substituting host reactive oxygen species (ROS) production. These ROS can act as second messengers and exert oxidative activity on proteins to influence immune, inflammatory, and other signaling processes. ROS and epigenetic mechanisms may have interactive effects as well. ROS, in addition to their role in signaling pathways and cellular redox alterations, also influence redox-sensitive transcription factors, thereby having an effect on gene expression. Specifically, ROS are involved in the activation of transcription factors, chromatin remodeling, and histone/protein deacetylation. These two proposed mechanisms correspond with the recent findings related to ASD, where a cofactor that is shown to be lower in ASD has antioxidative properties, responds to epigenetic modulation, and increases via microbiota interventions. The current evidence reviewed here suggests the need to update models of the gut-brain communication to include these two mechanisms. Such a modeling can also contribute to understanding the unknowns of host metabolism and physiology in ASD and afford potential therapeutic avenues for this as well as other psychiatric and physiological conditions.

Low-Dose Ionizing Radiation Exposure, Oxidative Stress and Epigenetic Programing of Health and Disease

Ionizing radiation exposure from medical diagnostic imaging has greatly increased over the last few decades. Approximately 80% of patients who undergo medical imaging are exposed to low-dose ionizing radiation (LDIR). Although there is widespread consensus regarding the harmful effects of high doses of radiation, the biological effects of low-linear energy transfer (LET) LDIR is not well understood. LDIR is known to promote oxidative stress, however, these levels may not be large enough to result in genomic mutations. There is emerging evidence that oxidative stress causes heritable modifications via epigenetic mechanisms (DNA methylation, histone modification, noncoding RNA regulation). These epigenetic modifications result in permanent cellular transformations without altering the underlying DNA nucleotide sequence. This review summarizes the major concepts in the field of epigenetics with a focus on the effects of low-LET LDIR (<100 mGy) and oxidative stress on epigenetic gene modification. In this review, we show evidence that suggests that LDIR-induced oxidative stress provides a mechanistic link between LDIR and epigenetic gene regulation. We also discuss the potential implication of LDIR exposure during pregnancy where intrauterine fetal development is highly susceptible to oxidative stress-induced epigenetic programing.

SIRT1, a Class III Histone Deacetylase, Regulates LPS-Induced Inflammation in Human Keratinocytes and Mediates the Anti-Inflammatory Effects of Hinokitiol

Skin inflammation is a response of the immune system to infection and injury. In this study, we report that hinokitiol, a tropolone-related natural compound that exhibits antioxidant, anti-inflammatory, and anticancer properties in various cell types, can modulate the inflammatory responses of primary human keratinocytes challenged with lipopolysaccharide (LPS). Hinokitiol treatment inhibited LPS-mediated up-regulation of proinflammatory factors including tumor necrosis factor alpha, IL-6, and prostaglandin E₂ (PGE₂). NF-κB activation and cell migration induced by LPS were blocked in keratinocytes treated with hinokitiol. Sirt1, a class Ⅲ histone deacetylase, was up-regulated by hinokitiol treatment, and the inhibition of Sirt1 activity using a pharmacological inhibitor or genetic silencing blocked hinokitiol-mediated anti-inflammatory effects. Further, hyperactivation of Sirt1 deacetylase using an adenoviral vector also attenuated LPS-induced inflammatory responses. We thus show that hinokitiol can attenuate LPS-mediated proinflammatory signals via Sirt1 histone deacetylase activation in primary human keratinocytes and suggest that hinokitiol may be a potential therapeutic agent in skin inflammatory diseases like psoriasis.

Discovery of a novel epigenetic cancer marker related to the oxidative status of human blood

Long-lasting oxidative stress exposure may lead to relatively stable epigenetic modifications of the DNA in order to activate anti-oxidative defence mechanisms. Oxidative stress related DNA methylation may therefore be associated (causally or as a by-product) with cancer. We measured derivatives of reactive oxygen metabolites (D-ROM), total thiol levels (TTL) and DNA methylation with the Illumina Infinium 450K BeadChip in three samples of German individuals aged ≥50 years: n = 1,000 ESTHER study baseline participants (DNA methylation only), n = 99 ESTHER eight-year follow-up participants and n = 142 participants of the BLITZ study. The correlation coefficient of methylation at cg10342304 and D-ROM in the ESTHER 8-year follow-up sample (r = -0.427; P = 1 × 10(-5)) was replicated with a P-value indicating statistical significance after correction for multiple testing in the BLITZ sample (r = -0.192; P = 0.022). The association was robust to adjusting for potential confounders. In the ESTHER baseline sample, the hazard ratio for cancer development in 11 years of follow-up comparing bottom and top quartile of DNA methylation at cg10342304 was 1.86 (95%-confidence-interval 1.01-3.43). In summary, this first epigenome-wide screening and replication study with oxidative status markers observed a negative correlation of D-ROM levels and DNA methylation at cg10342304 in two independent cohorts. This CpG site is located in the body region of the nucleoredoxin gene. The nucleoredoxin protein is a redox-dependent inhibitor of the Wnt/ß-catenin signaling pathway, a well-characterized cancer pathway. If the observed CpG-cancer association can be successfully replicated by other studies, this epigenetic marker could be an interesting biomarker of cancer risk.

The effects of the modulation of NMDA receptors by homocysteine thiolactone and dizocilpine on cardiodynamics and oxidative stress in isolated rat heart

In light of the limited data concerning the role of N-methyl-D-aspartate (NMDA) receptors in cardiac function, the aim of the present study was to determine the role of NMDA receptors in cardiac function, as well as the possible role played by the oxidative stress induced by the overstimulation of NMDA receptors in isolated rat heart. The hearts of male, Wistar albino rats (n = 24, 12 in each experimental group, BM 180-200 g) were retrogradely perfused at a constant perfusion pressure (70 cm H₂O₂), using the Langendorff technique, and cardiodynamic parameters were determined during the subsequent administration of DL-homocysteine thiolactone (DL-Hcy TLHC) alone, the combination of DL-Hcy TLHC and dizocilpine (MK-801), and MK-801 alone. In the second experimental group, the order of the administration of each of the substances was reversed. The oxidative stress biomarkers, including thiobarbituric acid reactive substances (TBARS), NO(2)(-), O(2)(-) and H₂O₂, were each determined spectrophotometrically. DL-Hcy TLHC and MK-801 depressed cardiac function. DL-Hcy TLHC decreased oxidative stress, a finding that contrasted with the results of the experiments in which MK-801 was administered first. The findings of this study were suggestive of the likely role played by NMDA receptors in the regulation of cardiac function and coronary circulation in isolated rat heart.

Mitochondria: a multimodal hub of hypoxia tolerance

Decreased oxygen availability impairs cellular energy production and, without a coordinated and matched decrease in energy consumption, cellular and whole organism death rapidly ensues. Of particular interest are mechanisms that protect brain from low oxygen injury, as this organ is not only the most sensitive to hypoxia, but must also remain active and functional during low oxygen stress. As a result of natural selective pressures, some species have evolved molecular and physiological mechanisms to tolerate prolonged hypoxia with no apparent detriment. Among these mechanisms are a handful of responses that are essential for hypoxia tolerance, including (i) sensors that detect changes in oxygen availability and initiate protective responses; (ii) mechanisms of energy conservation; (iii) maintenance of basic brain function; and (iv) avoidance of catastrophic cell death cascades. As the study of hypoxia-tolerant brain progresses, it is becoming increasingly apparent that mitochondria play a central role in regulating all of these critical mechanisms. Furthermore, modulation of mitochondrial function to mimic endogenous neuroprotective mechanisms found in hypoxia-tolerant species confers protection against otherwise lethal hypoxic stresses in hypoxia-intolerant organs and organisms. Therefore, lessons gleaned from the investigation of endogenous mechanisms of hypoxia tolerance in hypoxia-tolerant organisms may provide insight into clinical pathologies related to low oxygen stress.

Sirt1, a negative regulator of matrix metalloproteinase-9 in diabetic retinopathy

PURPOSE

In the pathogenesis of diabetic retinopathy, matrix metalloproteinase (MMP)-9 damages retinal mitochondria, activating the apoptotic machinery. Transcription of MMP-9 is regulated by nuclear factor kappa B (NF-κB), and the activation of NF-κB is modulated by the acetylation of its p65 subunit. Sirtuin 1 (Sirt1), a deacetylase, plays an important role in the acetylation-deacetylation of p65. The goal of this study is to investigate the role of Sirt1 in the activation of MMP-9 in diabetic retinopathy.

METHODS

The effect of hyperglycemia and Sirt1 activator, resveratrol, on acetylation of p65 and its binding at MMP-9 promoter-and mitochondrial damage and apoptosis-was assessed in the retinal endothelial cells. Role of oxidative stress in the regulation of Sirt1 was evaluated in the cells incubated in H2O2. The results were confirmed in the retina from diabetic mice with Sod2 or MMP-9 gene manipulated.

RESULTS

High glucose decreased Sirt1 activity and increased p65 acetylation, and resveratrol prevented increase in p65 acetylation, binding of p65 at MMP-9 promoter and MMP-9 activation, mitochondria damage, and cell apoptosis. While Sirt1 was decreased by H2O2, MMP-9 was significantly increased. Retina from wild-type diabetic mice presented similar decrease in Sirt1, and diabetic mice with Sod2 overexpression or MMP-9 deletion had normal retinal Sirt1. Retinal microvasculature from human donors with established diabetic retinopathy also had decreased Sirt1.

CONCLUSIONS

Thus, in diabetes, increase in oxidative stress inhibits Sirt1 and p65 is hyperacetylated, increasing the binding of p65 at MMP-9 promoter. Prevention of Sirt1 inhibition, via modulating acetylation of p65, should protect activation of MMP-9 and inhibit the development of diabetic retinopathy.

Dysregulation of histone acetyltransferases and deacetylases in cardiovascular diseases

Cardiovascular disease (CVD) remains a leading cause of mortality worldwide despite advances in its prevention and management. A comprehensive understanding of factors which contribute to CVD is required in order to develop more effective treatment options. Dysregulation of epigenetic posttranscriptional modifications of histones in chromatin is thought to be associated with the pathology of many disease models, including CVD. Histone acetyltransferases (HATs) and deacetylases (HDACs) are regulators of histone lysine acetylation. Recent studies have implicated a fundamental role of reversible protein acetylation in the regulation of CVDs such as hypertension, pulmonary hypertension, diabetic cardiomyopathy, coronary artery disease, arrhythmia, and heart failure. This reversible acetylation is governed by enzymes that HATs add or HDACs remove acetyl groups respectively. New evidence has revealed that histone acetylation regulators blunt cardiovascular and related disease states in certain cellular processes including myocyte hypertrophy, apoptosis, fibrosis, oxidative stress, and inflammation. The accumulating evidence of the detrimental role of histone acetylation in cardiac disease combined with the cardioprotective role of histone acetylation regulators suggests that the use of histone acetylation regulators may serve as a novel approach to treating the millions of patients afflicted by cardiac diseases worldwide.

Transcriptional regulation of yeast oxidative phosphorylation hypoxic genes by oxidative stress

AIMS

Mitochondrial cytochrome c oxidase (COX) subunit 5 and cytochrome c (Cyc) exist in two isoforms, transcriptionally regulated by oxygen in yeast. The gene pair COX5a/CYC1 encodes the normoxic isoforms (Cox5a and iso1-Cyc) and the gene pair COX5b/CYC7 encodes the hypoxic isoforms (Cox5b and iso2-Cyc). Rox1 is a transcriptional repressor of COX5b/CYC7 in normoxia. COX5b is additionally repressed by Ord1. Here, we investigated whether these pathways respond to environmental and mitochondria-generated oxidative stress.

RESULTS

The superoxide inducer menadione triggered a significant de-repression of COX5b and CYC7. Hydrogen peroxide elicited milder de-repression effects that were enhanced in the absence of Yap1, a key determinant in oxidative stress resistance. COX5b/CYC7 was also de-repressed in wild-type cells treated with antimycin A, a mitochondrial bc1 complex inhibitor that increases superoxide production. Exposure to menadione and H2O2 enhanced both, Hap1-independent expression of ROX1 and Rox1 steady-state levels without affecting Ord1. However, oxidative stress lowered the occupancy of Rox1 on COX5b and CYC7 promoters, thus inducing their de-repression.

INNOVATION

Reactive oxygen species (ROS)-induced hypoxic gene expression in normoxia involves the oxygen-responding Rox1 transcriptional machinery. Contrary to what occurs in hypoxia, ROS enhances Rox1 accumulation. However, its transcriptional repression capacity is compromised.

CONCLUSION

ROS induce expression of hypoxic COX5b and CYC7 genes through an Ord1- and Hap1-independent mechanism that promotes the release of Rox1 from or limits the access of Rox1 to its hypoxic gene promoter targets.

Combining redox-proteomics and epigenomics to explain the involvement of oxidative stress in psychiatric disorders

Psychiatric disorders affect approximately 10% of adults in North-America. The complex nature of these illnesses makes the search for their pathophysiology a challenge. However, studies have consistently shown that mitochondrial dysfunction and oxidative stress are common features across major psychiatric disorders, including bipolar disorder and schizophrenia. Nevertheless, little is known about specific targets of oxidation in the brain. The search for redox sensors (protein targets for oxidation) will offer information about which pathways are regulated by oxidation in psychiatric disorders. Additionally, DNA is also a target for oxidative damage and recently, studies have suggested that oxidation of cytosine and guanosine can serve as an epigenetic modulator by decreasing or preventing further DNA methylation. Therefore, this review aims to discuss how we can use redox-proteomics and epigenomics to help explain the role of oxidative damage in major psychiatric disorders, which may ultimately lead to the identification of targets for development of new medications.

Beta-mecaptoethanol suppresses inflammation and induces adipogenic differentiation in 3T3-F442A murine preadipocytes

Preadipocytes are present in adipose tissues throughout adult life that can proliferate and differentiate into mature adipocytes in response to environmental cues. Abnormal increase in adipocyte number or size leads to fat tissue expansion. However, it is now recognized that adipocyte hypertrophy is a greater risk factor for metabolic syndrome whereas fat tissue that continues to produce newer and smaller fat cells through preadipocyte differentiation is “metabolically healthy”. Because adipocyte hypertrophy is often associated with increased oxidant stress and low grade inflammation, both are linked to disturbed cellular redox, we tested how preadipocyte differentiation may be regulated by beta-mercaptoethanol (BME), a pharmacological redox regulator and radical scavenger, using murine 3T3-F442A preadipocytes as the cell model. Effects of BME on adipogenesis were measured by microphotography, real-time PCR, and Western analysis. Our data demonstrated that preadipocyte differentiation could be regulated by extracellular BME. At an optimal concentration, BME enhanced expression of adipogenic gene markers and lipid accumulation. This effect was associated with BME-mediated down-regulation of inflammatory cytokine expression during early differentiation. BME also attenuated TNFalpha-induced activation of NFkappaB in differentiating preadipocytes and partially restored TNFalpha-mediated suppression on adipogenesis. Using a non-adipogenic HEK293 cell line transfected with luciferase reporter genes, we demonstrated that BME reduced basal and TNFalpha-induced NFkappaB activity and increased basal and ciglitazone-induced PPARgamma activity; both may contribute to the pro-adipogenic effect of BME in differentiating F442A preadipocytes.

Caloric Restriction and the Nutrient-Sensing PGC-1α in Mitochondrial Homeostasis: New Perspectives in Neurodegeneration

Mitochondrial activity progressively declines during ageing and in many neurodegenerative diseases. Caloric restriction (CR) has been suggested as a dietary intervention that is able to postpone the detrimental aspects of aging as it ameliorates mitochondrial performance. This effect is partially due to increased mitochondrial biogenesis. The nutrient-sensing PGC-1α is a transcriptional coactivator that promotes the expression of mitochondrial genes and is induced by CR. It is believed that many of the mitochondrial and metabolic benefits of CR are due to increased PGC-1α activity. The increase of PGC-1α is also positively linked to neuroprotection and its decrement has been involved in the pathogenesis of many neurodegenerative diseases. This paper aims to summarize the current knowledge about the role of PGC-1α in neuronal homeostasis and the beneficial effects of CR on mitochondrial biogenesis and function. We also discuss how PGC-1α-governed pathways could be used as target for nutritional intervention to prevent neurodegeneration.

Environmental epigenetics: prospects for studying epigenetic mediation of exposure-response relationships

Changes in epigenetic marks such as DNA methylation and histone acetylation are associated with a broad range of disease traits, including cancer, asthma, metabolic disorders, and various reproductive conditions. It seems plausible that changes in epigenetic state may be induced by environmental exposures such as malnutrition, tobacco smoke, air pollutants, metals, organic chemicals, other sources of oxidative stress, and the microbiome, particularly if the exposure occurs during key periods of development. Thus, epigenetic changes could represent an important pathway by which environmental factors influence disease risks, both within individuals and across generations. We discuss some of the challenges in studying epigenetic mediation of pathogenesis and describe some unique opportunities for exploring these phenomena.

Targeting microglia-mediated neurotoxicity: the potential of NOX2 inhibitors

Microglia are key sentinels of central nervous system health, and their dysfunction has been widely implicated in the progressive nature of neurodegenerative diseases. While microglia can produce a host of factors that are toxic to neighboring neurons, NOX2 has been implicated as a common and essential mechanism of microglia-mediated neurotoxicity. Accumulating evidence indicates that activation of the NOX2 enzyme complex in microglia is neurotoxic, both through the production of extracellular reactive oxygen species that damage neighboring neurons as well as the initiation of redox signaling in microglia that amplifies the pro-inflammatory response. More specifically, evidence supports that NOX2 redox signaling enhances microglial sensitivity to pro-inflammatory stimuli, and amplifies the production of neurotoxic cytokines, to promote chronic and neurotoxic microglial activation. Here, we describe the evidence denoting the role of NOX2 in microglia-mediated neurotoxicity with an emphasis on Alzheimer's and Parkinson's disease, describe available inhibitors that have been tested, and detail evidence of the neuroprotective and therapeutic potential of targeting this enzyme complex to regulate microglia.

Physiological effects of Type 2 diabetes on mRNA processing and gene expression

Characteristics of Type 2 diabetes include both high blood glucose (hyperglycemia) and raised cholesterol and triglycerides (hyperlipidemia). Several studies have now shown that both hyperglycemia and hyperlipidemia can alter gene expression by disrupting physiological mechanisms of gene regulation, including alternative mRNA splicing, epigenetic gene regulation and miRNA-mediated regulation of gene expression. These processes may also be influenced by intracellular oxidative stress, which is increased in diabetes and in response to hyperglycemia and hyperlipidemia. Many pathways relevant to diabetes are affected by altered gene expression, including lipid and glucose metabolism and oxidative phosphorylation. This article considers how hyperglycemia and hyperlipidemia can alter gene expression in diabetes, which could potentially contribute to the worsening of the diabetic phenotype and diabetic complications.