Hormonal and chemical regulation of paraoxonases in mice

Dietary proteins modulate high-density lipoprotein characteristics in a sex-specific way in Apoe-deficient mice

OBJECTIVES

The type and amount of dietary protein have become a topic of renewed interest, considering their involvement in several diseases. However, little attention has been devoted to the effect of avian proteins despite their wide human consumption. In a previous study, we saw that compared with soybean protein, the consumption of avian proteins, depending on sex, resulted in similar or lower atherosclerosis with a higher paraoxonase 1 activity, an antioxidant enzyme carried by high-density lipoproteins (HDL). This suggests that under these conditions, the HDL lipoproteins may undergo important changes. The aim of this research was to study the influence of soybean, chicken, and turkey proteins on the characteristics of HDL.

METHODS

Male and female Apoe-deficient mice were fed purified Western diets based on the AIN-93 diet, differing only in the protein source, for 12 wk. After this period, blood and liver samples were taken for analysis of HDL composition and hepatic expression of genes related to HDL metabolism (Abca1, Lcat, Pltp, Pon1, and Scarb1). Depending on sex, these genes define a different network of interactions. Females consuming the turkey protein-containing diet showed decreased atherosclerotic foci, which can be due to larger very-low-density lipoproteins (VLDLs) calculated by molar ratio triacylglycerols/VLDL cholesterol and higher expression of Lcat. In contrast, in males, a higher ratio of paraoxonase1 to apolipoprotein A1 decreased the oxidative status of the different lipoproteins, and augmented Abca1 expression was observed.

CONCLUSIONS

The source of protein has an effect on the development of atherosclerosis depending on sex by modifying HDL characteristics and the expression of genes involved in their properties.

Paraoxonases at the Heart of Neurological Disorders

Paraoxonase enzymes serve as an important physiological redox system that participates in the protection against cellular injury caused by oxidative stress. The PON enzymes family consists of three members (PON-1, PON-2, and PON-3) that share a similar structure and location as a cluster on human chromosome 7. These enzymes exhibit anti-inflammatory and antioxidant properties with well-described roles in preventing cardiovascular disease. Perturbations in PON enzyme levels and their activity have also been linked with the development and progression of many neurological disorders and neurodegenerative diseases. The current review summarizes the available evidence on the role of PONs in these diseases and their ability to modify risk factors for neurological disorders. We present the current findings on the role of PONs in Alzheimer's disease, Parkinson's disease, and other neurodegenerative and neurological diseases.

Modulatory Effect of Lifestyle-Related, Environmental and Genetic Factors on Paraoxonase-1 Activity: A Review

Paraoxonase-1 (PON1) is a calcium-dependent, HDL-bound serum hydrolase active toward a wide variety of substrates. PON1 displays three types of activities, among which lactonase, paraoxonase, arylesterase and phosphotriesterase can be distinguished. Not only is this enzyme a major organophosphate compound detoxifier, but it is also an important constituent of the cellular antioxidant system and has anti-inflammatory and antiatherogenic functions. The concentration and activity of PON1 is highly variable among individuals, and these differences can be both of genetic origin and be a subject of epigenetic regulation. Owing to the fact that, in recent decades, the exposure of humans to an increasing number of different xenobiotics has been continuously rising, the issues concerning the role and activity of PON1 shall be reconsidered with particular attention to growing pharmaceuticals intake, dietary habits and environmental awareness. In the following manuscript, the current state of knowledge concerning the influence of certain modifiable and unmodifiable factors, including smoking, alcohol intake, gender, age and genotype variation on PON1 activity, along with pathways through which these could interfere with the enzyme's protective functions, is presented and discussed. Since exposure to certain xenobiotics plays a key role in PON1 activity, the influence of organophosphates, heavy metals and several pharmaceutical agents is also specified.

Insights into the role of paraoxonase 2 in human pathophysiology

Paraoxonase 2 (PON2) is a ubiquitously expressed intracellular enzyme that is known to have a protective role from oxidative stress. Clinical studies have also demonstrated the significance of PON2 in the manifestation of cardiovascular and several other diseases, and hence, it is considered an important biomarker. Recent findings of its expression in brain tissue suggest its potential protective effect on oxidative stress and neuroinflammation. Polymorphisms of PON2 in humans are a risk factor in many pathological conditions, suggesting a possible mechanism of its anti-oxidative property probably through lactonase activity. However, exogenous factors may also modulate the expression and activity of PON2. Hence, this review aims to report the mechanism by which PON2 expression is regulated and its role in oxidative stress disorders such as neurodegeneration and tumor formation. The role of PON2 owing to its lactonase activity in bacterial infectious diseases and association of PON2 polymorphism with pathological conditions are also highlighted.

Insights into the role of paraoxonase 2 in human pathophysiology

Paraoxonase 2 (PON2) is a ubiquitously expressed intracellular enzyme that is known to have a protective role from oxidative stress. Clinical studies have also demonstrated the significance of PON2 in the manifestation of cardiovascular and several other diseases, and hence, it is considered an important biomarker. Recent findings of its expression in brain tissue suggest its potential protective effect on oxidative stress and neuroinflammation. Polymorphisms of PON2 in humans are a risk factor in many pathological conditions, suggesting a possible mechanism of its anti-oxidative property probably through lactonase activity. However, exogenous factors may also modulate the expression and activity of PON2. Hence, this review aims to report the mechanism by which PON2 expression is regulated and its role in oxidative stress disorders such as neurodegeneration and tumor formation. The role of PON2 owing to its lactonase activity in bacterial infectious diseases and association of PON2 polymorphism with pathological conditions are also highlighted.

Prevalence and mortality of COVID-19 are associated with the L55M functional polymorphism of Paraoxonase 1

Introduction

Accumulating evidence recommends that infectious diseases including coronavirus disease 2019 (COVID-19) are often associated with oxidative stress and inflammation. Paraoxonase 1 (PON1, OMIM: 168,820), a member of the paraoxonase gene family, has antioxidant properties. Enzyme activity of paraoxonase depends on a variety of influencing factors such as polymorphisms of PON1, ethnicity, gender, age, and a number of environmental variables. The PON1 has two common functional polymorphisms, namely, Q192R (rs662) and L55M (rs854560). The R192 and M55 alleles are associated with increase and decrease in enzyme activity, respectively.

Objective

The present study was conducted to investigate the possible association of rs662 and rs854560 polymorphisms with morbidity and mortality of COVID-19.

Methods

Data for the prevalence, mortality, and amount of accomplished diagnostic test (per 10⁶ people) on 25 November 2020 from 48 countries were included in the present study. The Human Development Index (HDI) was used as a potential confounding variable.

Results

The frequency of M55 was positively correlated with the prevalence (partial r = 0.487, df = 36, p = 0.002) and mortality of COVID-19 (partial r = 0.551, df = 36, p < 0.001), after adjustments for HDI and amount of the accomplished diagnostic test as possible confounders.

Conclusions

This means that countries with higher M55 frequency have higher prevalence and mortality of COVID-19.

The 2-hydroxy-nevirapine metabolite as a candidate for boosting apolipoprotein A1 and for modulating anti-HDL antibodies

The antiretroviral nevirapine (NVP) is associated to a reduction of atherosclerotic lesions and increases in high-density lipoprotein (HDL)-cholesterol. Despite being a hepatotoxic drug, which forbids its re-purposing to other therapeutic areas, not all NVP metabolites have the same potential to induce toxicity. Our aim was to investigate the effects of NVP and its metabolites in an exploratory study, towards the identification of a candidate to boost HDL. A pilot prospective (n = 11) and a cross-sectional (n = 332) clinical study were performed with the following endpoints: HDL-cholesterol and apolipoprotein A1 (ApoA1) levels, anti-HDL and anti-ApoA1 antibodies titers, paraoxonase, arylesterase and lactonase activities of paraoxonase-1, and NVP's metabolite profile. NVP treatment increased HDL-cholesterol, ApoA1 and paraoxonase-1 activities, and lowered anti-HDL and anti-ApoA1 titers. In the prospective study, the temporal modulation induced by NVP was different for each HDL-related endpoint. The first observation was a decrease in the anti-HDL antibodies titers. In the cross-sectional study, the lower titers of anti-HDL antibodies were associated to the proportion of 2-hydroxy-NVP (p = 0.03). In vitro models of hepatocytes were employed to clarify the individual contribution of NVP's metabolites for ApoA1 modulation. Long-term incubations of NVP and 2-hydroxy-NVP in the metabolically competent 3D model caused an increase in ApoA1 reaching 43 % (p < 0.05) and 86 % (p < 0.001), respectively. These results support the contribution of drug biotransformation for NVP-induced HDL modulation, highlighting the role of 2-hydroxy-NVP as ApoA1 booster and its association to lower anti-HDL titers. This biotransformation-guided approach allowed us to identify a non-toxic NVP metabolite as a candidate for targeting HDL.

Sex Difference Impacts on the Relationship between Paraoxonase-1 (PON1) and Type 2 Diabetes

Type-2 diabetes (T2D) and its cardiovascular complications are related to sex. Increasing evidence suggests that paraoxonase 1 (PON1) activity, an antioxidant enzyme bound to high-density lipoproteins (HDL), is implicated in the onset and clinical progression of T2D. Since we previously showed that PON1 is a sexual dimorphic protein, we now investigated whether sex might impact the relationship between PON1 and this chronic disease. To address this aim, we assessed PON1 activity in the sera of 778 patients, including controls (women, n = 383; men, n = 198) and diabetics (women, n = 79; men = 118). PON1 activity decreased in both women and men with T2D compared with controls (p < 0.05 and p > 0.001, respectively), but the change was 50% larger in the female cohort. In line with this result, the enzyme activity was associated with serum glucose level only in women (r = -0.160, p = 0.002). Notably, only within this gender category, lower PON1 activity was independently associated with increased odds of being diabetic (odds ratio (95% Confidence interval: 2.162 (1.075-5.678)). In conclusion, our study suggests that PON1-deficiency in T2D is a gender-specific phenomenon, with women being more affected than men. This could contribute to the partial loss of female cardiovascular advantage associated with T2D.

Genetic resistance to DEHP-induced transgenerational endocrine disruption

Di(2-ethylhexyl)phthalate (DEHP) interferes with sex hormones signaling pathways (SHP). C57BL/6J mice prenatally exposed to 300 mg/kg/day DEHP develop a testicular dysgenesis syndrome (TDS) at adulthood, but similarly-exposed FVB/N mice are not affected. Here we aim to understand the reasons behind this drastic difference that should depend on the genome of the strain. In both backgrounds, pregnant female mice received per os either DEHP or corn oil vehicle and the male filiations were examined. Computer-assisted sperm analysis showed a DEHP-induced decreased sperm count and velocities in C57BL/6J. Sperm RNA sequencing experiments resulted in the identification of the 62 most differentially expressed RNAs. These RNAs, mainly regulated by hormones, produced strain-specific transcriptional responses to prenatal exposure to DEHP; a pool of RNAs was increased in FVB, another pool of RNAs was decreased in C57BL/6J. In FVB/N, analysis of non-synonymous single nucleotide polymorphisms (SNP) impacting SHP identified rs387782768 and rs29315913 respectively associated with absence of the Forkhead Box A3 (Foxa3) RNA and increased expression of estrogen receptor 1 variant 4 (NM_001302533) RNA. Analysis of the role of SNPs modifying SHP binding sites in function of strain-specific responses to DEHP revealed a DEHP-resistance allele in FVB/N containing an additional FOXA1-3 binding site at rs30973633 and four DEHP-induced beta-defensins (Defb42, Defb30, Defb47 and Defb48). A DEHP-susceptibility allele in C57BL/6J contained five SNPs (rs28279710, rs32977910, rs46648903, rs46677594 and rs48287999) affecting SHP and six genes (Svs2, Svs3b, Svs4, Svs3a, Svs6 and Svs5) epigenetically silenced by DEHP. Finally, targeted experiments confirmed increased methylation in the Svs3ab promoter with decreased SEMG2 persisting across generations, providing a molecular explanation for the transgenerational sperm velocity decrease found in C57BL/6J after DEHP exposure. We conclude that the existence of SNP-dependent mechanisms in FVB/N inbred mice may confer resistance to transgenerational endocrine disruption.

A non-synonymous single nucleotide polymorphism in the paraoxonase 3 gene regulates meat quality in Berkshire pigs

The paraoxonase (Pon) gene family contains three members: Pon1, Pon2, and Pon3. Pon3 modulates superoxide production and prevents apoptosis. The role of Pon3 has not been fully elucidated in the pig. This study is the first to investigate the association between Pon3 and meat quality in the Berkshire pig. We identified a single nucleotide polymorphism in the Pon3 gene (c.227A > G) that resulted in a change in histidine to arginine at position 76. To elucidate the role of this non-synonymous single nucleotide polymorphism in the Pon3 gene, we analysed the Pon3 genotype and meat quality traits in 434 Berkshire pigs. The results of a codominant model show that carcass weight, meat colour (lightness), cooking loss, and the Warner–Bratzler shear force were significantly associated with the Pon3 genotype. Furthermore, the 24-h post-mortem pH had the strongest relationship with the Pon3 genotype. The G allele decreased cooking loss and fat content, whereas the A allele increased the 24-h post-mortem pH and decreased backfat thickness, which contribute to meat storage life and M. longissimus dorsi depth respectively. In conclusion, the non-synonymous single nucleotide polymorphism in the Pon3 gene showed a close correlation with meat quality traits in the Berkshire pig.

RNA-Seq reveals common and unique PXR- and CAR-target gene signatures in the mouse liver transcriptome

The pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are well-known xenobiotic-sensing nuclear receptors with overlapping functions. However, there lacks a quantitative characterization to distinguish between the PXR and CAR target genes and signaling pathways in the liver. The present study performed a transcriptomic comparison of the PXR- and CAR-targets using RNA-Seq in livers of adult wild-type mice that were treated with the prototypical PXR ligand PCN (200mg/kg, i.p. once daily for 4days in corn oil) or the prototypical CAR ligand TCPOBOP (3mg/kg, i.p., once daily for 4days in corn oil). At the given doses, TCPOBOP differentially regulated many more genes (2125) than PCN (212), and 147 of the same genes were differentially regulated by both chemicals. As expected, the top pathways differentially regulated by both PCN and TCPOBOP were involved in xenobiotic metabolism, and they also up-regulated genes involved in retinoid metabolism, but down-regulated genes involved in inflammation and iron homeostasis. Regarding unique pathways, PXR activation appeared to overlap with the aryl hydrocarbon receptor signaling, whereas CAR activation appeared to overlap with the farnesoid X receptor signaling, acute-phase response, and mitochondrial dysfunction. The mRNAs of differentially regulated drug-processing genes (DPGs) partitioned into three patterns, namely TCPOBOP-induced, PCN-induced, as well as TCPOBOP-suppressed gene clusters. The cumulative mRNAs of the differentially regulated DPGs, phase-I and -II enzymes, as well as efflux transporters were all up-regulated by both PCN and TCPOBOPOP, whereas the cumulative mRNAs of the uptake transporters were down-regulated only by TCPOBOP. The absolute mRNA abundance in control and receptor-activated conditions was examined in each DPG category to predict the contribution of specific DPG genes in the PXR/CAR-mediated pharmacokinetic responses. The preferable differential regulation by TCPOBOP in the entire hepatic transcriptome correlated with a marked change in the expression of many DNA and histone epigenetic modifiers. In conclusion, the present study has revealed known and novel, as well as common and unique targets of PXR and CAR in mouse liver following pharmacological activation using their prototypical ligands. Results from this study will further support the role of these receptors in regulating the homeostasis of xenobiotic and intermediary metabolism in the liver, and aid in distinguishing between PXR and CAR signaling at various physiological and pathophysiological conditions. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

Impact of the X Chromosome and sex on regulatory variation

The X Chromosome, with its unique mode of inheritance, contributes to differences between the sexes at a molecular level, including sex-specific gene expression and sex-specific impact of genetic variation. Improving our understanding of these differences offers to elucidate the molecular mechanisms underlying sex-specific traits and diseases. However, to date, most studies have either ignored the X Chromosome or had insufficient power to test for the sex-specific impact of genetic variation. By analyzing whole blood transcriptomes of 922 individuals, we have conducted the first large-scale, genome-wide analysis of the impact of both sex and genetic variation on patterns of gene expression, including comparison between the X Chromosome and autosomes. We identified a depletion of expression quantitative trait loci (eQTL) on the X Chromosome, especially among genes under high selective constraint. In contrast, we discovered an enrichment of sex-specific regulatory variants on the X Chromosome. To resolve the molecular mechanisms underlying such effects, we generated chromatin accessibility data through ATAC-sequencing to connect sex-specific chromatin accessibility to sex-specific patterns of expression and regulatory variation. As sex-specific regulatory variants discovered in our study can inform sex differences in heritable disease prevalence, we integrated our data with genome-wide association study data for multiple immune traits identifying several traits with significant sex biases in genetic susceptibilities. Together, our study provides genome-wide insight into how genetic variation, the X Chromosome, and sex shape human gene regulation and disease.

Developmental expression of paraoxonase 2

Paraoxonase 2 (PON2) is a member of the paraoxonase gene family also comprising PON1 and PON3. PON2 functions as a lactonase and exhibits anti-bacterial as well as antioxidant properties. At the cellular level, PON2 localizes to the mitochondrial and endoplasmic reticulum membranes where it scavenges reactive oxygen species. PON2 is of particular interest as it is the only paraoxonase expressed in brain tissue and appears to play a critical role in mitigating oxidative stress in the brain. The aim of this study was to investigate the expression of PON2 at the protein and mRNA level in the brain and liver of mice through development to identify potential age windows of susceptibility to oxidative stress, as well as to compare expression of hepatic PON2 to expression of PON1 and PON3. Overall, PON2 expression in the brain was lower in neonatal mice and increased with age up to postnatal day (PND) 21, with a significant decrease observed at PND 30 and 60. In contrast, the liver showed continuously increasing levels of PON2 with age, similar to the patterns of PON1 and PON3. PON2 protein levels were also investigated in brain samples from non-human primates, with PON2 increasing with age up to the infant stage and decreasing at the juvenile stage, mirroring the results observed in the mouse brain. These variable expression levels of PON2 suggest that neonatal and young adult animals may be more susceptible to neurological insult by oxidants due to lower levels of PON2 in the brain.

RNA Sequencing Quantification of Xenobiotic-Processing Genes in Various Sections of the Intestine in Comparison to the Liver of Male Mice

Previous reports on tissue distribution of xenobiotic-processing genes (XPGs) have limitations, because many non-cytochrome P450 phase I enzymes have not been investigated, and one cannot compare the real mRNA abundance of multiple XPGs using conventional quantification methods. Therefore, this study aimed to quantify and compare the mRNA abundance of all major XPGs in the liver and intestine using RNA sequencing. The mRNA profiles of 304 XPGs, including phase I, phase II enzymes, phase II cosubstrate synthetic enzymes, xenobiotic transporters, as well as xenobiotic-related transcription factors, were systematically examined in the liver and various sections of the intestine in adult male C57BL/6J mice. By two-way hierarchical clustering, over 80% of the XPGs had tissue-divergent expression, which partitioned into liver-predominant, small intestine-predominant, and large intestine-predominant patterns. Among the genes, 54% were expressed highest in the liver, 21% in the duodenum, 4% in the jejunum, 6% in the ileum, and 15% in the large intestine. The highest-expressed XPG in the liver was Mgst1; in the duodenum, Cyp3a11; in the jejunum and ileum, Ces2e; and in the large intestine, Cyp2c55. Interestingly, XPGs in the same family usually exhibited highly different tissue distribution patterns, and many XPGs were almost exclusively expressed in one tissue and minimally expressed in others. In conclusion, the present study is among the first and the most comprehensive investigations of the real mRNA abundance and tissue-divergent expression of all major XPGs in mouse liver and intestine, which aids in understanding the tissue-specific biotransformation and toxicity of drugs and other xenobiotics.

Species differences in paraoxonase mediated hydrolysis of several organophosphorus insecticide metabolites

Paraoxonase (PON1) is a calcium dependent enzyme that is capable of hydrolyzing organophosphate anticholinesterases. PON1 activity is present in most mammals and previous research established that PON1 activity differs depending on the species. These studies mainly used the organophosphate substrate paraoxon, the active metabolite of the insecticide parathion. Using serum PON1 from different mammalian species, we compared the hydrolysis of paraoxon with the hydrolysis of the active metabolites (oxons) of two additional organophosphorus insecticides, methyl parathion and chlorpyrifos. Paraoxon hydrolysis was greater than that of methyl paraoxon, but the level of activity between species displayed a similar pattern. Regardless of the species tested, the hydrolysis of chlorpyrifos-oxon was significantly greater than that of paraoxon or methyl paraoxon. These data indicate that chlorpyrifos-oxon is a better substrate for PON1 regardless of the species. The pattern of species differences in PON1 activity varied with the change in substrate to chlorpyrifos-oxon from paraoxon or methyl paraoxon. For example, the sex difference observed here and reported elsewhere in the literature for rat PON1 hydrolysis of paraoxon was not present when chlorpyrifos-oxon was the substrate.

Paraoxonase enzyme protects retinal pigment epithelium from chlorpyrifos insult

Retinal pigment epithelium (RPE) provides nourishment and protection to the eye. RPE dysfunction due to oxidative stress and inflammation is one of the major reason for many of the retinal disorders. Organophosphorus pesticides are widely used in the agricultural, industrial and household activities in India. However, their effects on the eye in the context of RPE has not been studied. In this study the defense of the ARPE19 cells exposed to Chlorpyrifos (1 nM to 100 µM) in terms of the enzyme paraoxonase (PON) was studied at 24 hr and 9 days of treatment. Chlorpyrifos was found to induce oxidative stress in the ARPE19 cells as seen by significant increase in ROS and decrease in glutathione (GSH) levels without causing cell death. Tissue resident Paraoxonase 2 (PON2) mRNA expression was elevated with chlorpyrifos exposure. The three enzymatic activities of PON namely, paraoxonase (PONase), arylesterase (PON AREase) and thiolactonase (PON HCTLase) were also found to be significantly altered to detoxify and as an antioxidant defense. Among the transcription factors regulating PON2 expression, SP1 was significantly increased with chlorpyrifos exposure. PON2 expression was found to be crucial as ARPE19 cells showed a significant loss in their ability to withstand oxidative stress when the cells were subjected to chlorpyrifos after silencing PON2 expression. Treatment with N-acetyl cysteine positively regulated the PON 2 expression, thus promoting the antioxidant defense put up by the cells in response to chlorpyrifos.

Pharmacogenetics of paraoxonase activity: elucidating the role of high-density lipoprotein in disease

PON1 is a key component of high-density lipoproteins (HDLs) and is at least partially responsible for HDL's antioxidant/atheroprotective properties. PON1 is also associated with numerous human diseases, including cardiovascular disease, Parkinson's disease and cancer. In addition, PON1 metabolizes a broad variety of substrates, including toxic organophosphorous compounds, statin adducts, glucocorticoids, the likely atherogenic L-homocysteine thiolactone and the quorum-sensing factor of Pseudomonas aeruginosa. Numerous cardiovascular and antidiabetic pharmacologic agents, dietary macronutrients, lifestyle factors and antioxidant supplements affect PON1 expression and enzyme activity levels. Owing to the importance of PON1 to HDL function and its individual association with diverse human diseases, pharmacogenomic interactions between PON1 and the various factors that alter its expression and activity may represent an important therapeutic target for future investigation.

Lack of ligand-selective binding of the aryl hydrocarbon receptor to putative DNA binding sites regulating expression of Bax and paraoxonase 1 genes

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the biological and toxicological effects of structurally diverse chemicals through its ability to bind specific DNA recognition sites (dioxin responsive elements (DREs)), and activate transcription of adjacent genes. While the DRE has a highly conserved consensus sequence, it has been suggested that the nucleotide specificity of AhR DNA binding may be ligand-dependent. The upstream regulatory regions of the murine Bax and human paraoxonase 1 (PON1) genes reportedly contain unique DRE-like sequences that respond to AhRs activated by some ligands but not others. Given the significant implications of this observation to understanding the diversity in AhR responses and that of other ligand-dependent nuclear receptors, a combination of DNA binding, nuclear translocation and gene expression analysis was used to investigate the molecular mechanisms underlying these ligand-selective responses. Although known AhR agonists stimulated AhR nuclear translocation, DRE binding and gene expression, the ligand-selective DRE-like DNA elements identified in the Bax and PON1 upstream regulatory regions failed to bind ligand-activated AhR or confer AhR-responsiveness upon a reporter gene. These results argue against the reported ligand-selectivity of AhR DNA binding and suggest DNA binding by ligand activated AhR involves DRE-containing DNA.

Macrophage paraoxonase 2 regulates calcium homeostasis and cell survival under endoplasmic reticulum stress conditions and is sufficient to prevent the development of aggravated atherosclerosis in paraoxonase 2 deficiency/apoE-/- mice on a Western diet

Paraoxonase 2 deficiency (PON2-def) alters mitochondrial function and exacerbates the development of atherosclerosis in mice. PON2 overexpression protects against ER stress in cell culture. In this paper, we examined the role of PON2 in the unexplored link between ER stress and mitochondrial dysfunction and tested whether restoration of PON2 in macrophages is sufficient to reduce aggravated atherosclerosis in PON2-def/apoE(-/-) mice on a Western diet. ER stress response genes, intracellular calcium levels, and apoptotic nuclei were significantly elevated in PON2-def/apoE(-/-) macrophages compared to apoE(-/-) macrophages in response to ER stressors, but not at the basal level. In contrast, PON2-def/apoE(-/-) macrophages exhibited greater mitochondrial stress at the basal level, which was further worsened in response to ER stressors. There was no difference in ER stress response genes and apoptotic nuclei between apoE(-/-) and PON2-def/apoE(-/-) macrophages when pretreated with xestospongin (which blocks the release of calcium from ER) suggesting that PON2 modulates cell survival and ER stress by maintaining calcium homeostasis. Treatment with a mitochondrial calcium uptake inhibitor, RU360, attenuated ER stressor mediated mitochondrial dysfunction in PON2-def/apoE(-/-) macrophages. CHOP expression (ER stress marker) and apoptotic nuclei were significantly higher in aortic lesions of PON2-def/apoE(-/-) mice compared to apoE(-/-) mice fed a Western diet. Restoration of PON2 in macrophages reduced ER stress, mitochondrial dysfunction and apoptosis in response to ER stressors. Furthermore, restoration of PON2 in macrophages reduced lesional apoptosis and atherosclerosis in PON2-def/apoE(-/-) mice on a Western diet. Our data suggest that macrophage PON2 modulates mechanisms that link ER stress, mitochondrial dysfunction and the development of atherosclerosis.