The detrimental health effects of traffic-related air pollution: a role for DNA methylation?

Lupus, DNA Methylation, and Air Pollution: A Malicious Triad

The pathogenesis of systemic lupus erythematosus (SLE) remains elusive to this day; however, genetic, epigenetic, and environmental factors have been implicated to be involved in disease pathogenesis. Recently, it was demonstrated that in systemic lupus erythematosus (SLE) patients, interferon-regulated genes are hypomethylated in naïve CD4+ T cells, CD19+ B lymphocytes, and CD14+ monocytes. This suggests that interferon-regulated genes may have been epigenetically poised in SLE patients for rapid expression upon stimulation by different environmental factors. Additionally, environmental studies have identified DNA (hypo)methylation changes as a potential mechanism of environmentally induced health effects in utero, during childhood and in adults. Finally, epidemiologic studies have firmly established air pollution as a crucial SLE risk factor, as studies showed an association between fine particulate matter (PM2.5) and traditional SLE biomarkers related to disease flare, hospital admissions, and an increased SLEDAI score. In this review, the relationship between aberrant epigenetic regulation, the environment, and the development of SLE will be discussed.

First trimester exposure to ambient gaseous air pollutants and risk of orofacial clefts: a case-control study in Changsha, China

Background

A growing body of studies have investigated the association between air pollution exposure during early pregnancy and the risk of orofacial clefts, but these studies put more emphasis on particulate matter and reported inconsistent results, while research on the independent effects of gaseous air pollutants on orofacial clefts has been quite inadequate, especially in China.

Methods

A case–control study was conducted in Changsha, China from 2015 to 2018. A total of 446 cases and 4460 controls were included in the study. Daily concentrations of CO, NO₂, SO₂, O₃, PM_2.5 and PM₁₀ during the first trimester of pregnancy were assigned to each subject using the nearest monitoring station method. Multivariate logistic regression models were applied to evaluate the associations of monthly average exposure to gaseous air pollutants with orofacial clefts and its subtypes before and after adjusting for particulate matter. Variance inflation factors (VIFs) were used to determine if the effects of gaseous air pollutants could be independent of particulate matter.

Results

Increase in CO, NO₂ and SO₂ significantly increased the risk of cleft lip with or without cleft palate (CL/P) in all months during the first trimester of pregnancy, with aORs ranging from 1.39 to 1.48, from 1.35 to 1.61 and from 1.22 to 1.35, respectively. The risk of cleft palate only (CPO) increased with increasing NO₂ exposure levels in the first trimester of pregnancy, with aORs ranging from 1.60 to 1.66. These effects sustained and even exacerbated after adjusting for particulate matter. No significant effect of O₃ was observed.

Conclusions

Our study suggested that maternal exposure to CO, NO₂, and SO₂ during the first trimester of pregnancy might contribute to the development of orofacial clefts, and the associations were potentially independent of particulate matter.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01876-7.

Acute changes in DNA methylation in relation to 24 h personal air pollution exposure measurements: A panel study in four European countries

BACKGROUND

One of the potential mechanisms linking air pollution to health effects is through changes in DNA-methylation, which so far has mainly been analyzed globally or at candidate sites.

OBJECTIVE

We investigated the association of personal and ambient air pollution exposure measures with genome-wide DNA-methylation changes.

METHODS

We collected repeated 24-hour personal and ambient exposure measurements of particulate matter (PM2.5), PM2.5 absorbance, and ultrafine particles (UFP) and peripheral blood samples from a panel of 157 healthy non-smoking adults living in four European countries. We applied univariate mixed-effects models to investigate the association between air pollution and genome-wide DNA-methylation perturbations at single CpG (cytosine-guanine dinucleotide) sites and in Differentially Methylated Regions (DMRs). Subsequently, we explored the association of air pollution-induced methylation alterations with gene expression and serum immune marker levels measured in the same subjects.

RESULTS

Personal exposure to PM2.5 was associated with methylation changes at 13 CpG sites and 69 DMRs. Two of the 13 identified CpG sites (mapped to genes KNDC1 and FAM50B) were located within these DMRs. In addition, 42 DMRs were associated with personal PM2.5 absorbance exposure, 16 DMRs with personal exposure to UFP, 4 DMRs with ambient exposure to PM2.5, 16 DMRs with ambient PM2.5 absorbance exposure, and 15 DMRs with ambient UFP exposure. Correlation between methylation levels at identified CpG sites and gene expression and immune markers was generally moderate.

CONCLUSION

This study provides evidence for an association between 24-hour exposure to air pollution and DNA-methylation at single sites and regional clusters of CpGs. Analysis of differentially methylated regions provides a promising avenue to further explore the subtle impact of environmental exposures on DNA-methylation.

Maternal Exposure to Nitrogen Dioxide, Intake of Methyl Nutrients, and Congenital Heart Defects in Offspring

Nutrients that regulate methylation processes may modify susceptibility to the effects of air pollutants. Data from the National Birth Defects Prevention Study (United States, 1997-2006) were used to estimate associations between maternal exposure to nitrogen dioxide (NO2), dietary intake of methyl nutrients, and the odds of congenital heart defects in offspring. NO2 concentrations, a marker of traffic-related air pollution, averaged across postconception weeks 2-8, were assigned to 6,160 nondiabetic mothers of cases and controls using inverse distance-squared weighting of air monitors within 50 km of maternal residences. Intakes of choline, folate, methionine, and vitamins B6 and B12 were assessed using a food frequency questionnaire. Hierarchical regression models, which accounted for similarities across defects, were constructed, and relative excess risks due to interaction were calculated. Relative to women with the lowest NO2 exposure and high methionine intake, women with the highest NO2 exposure and lowest methionine intake had the greatest odds of offspring with a perimembranous ventricular septal defect (odds ratio = 3.23, 95% confidence interval: 1.74, 6.01; relative excess risk due to interaction = 2.15, 95% confidence interval: 0.39, 3.92). Considerable departure from additivity was not observed for other defects. These results provide modest evidence of interaction between nutrition and NO2 exposure during pregnancy.

Dose- and time- effect responses of DNA methylation and histone H3K9 acetylation changes induced by traffic-related air pollution

As an important risk factor of respiratory disorders, traffic-related air pollution (TRAP) has caused extensive concerns. Epigenetic change has been considered a link between TRAP and respiratory diseases. However, the exact effects of TRAP on epigenetic changes are still unclear. Here we investigated the dose- and time- effect responses of TRAP on DNA methylations and H3K9 acetylation (H3K9ac) in both blood and lung tissues of rats. The findings showed that every 1 μg/m³ increase of TRAP components were associated with changes in %5 mC (95% CI) in LINE-1, iNOS, p16^CDKN2A, and APC ranging from −0.088% (−0.150, −0.026) to 0.102 (0.049, 0.154), as well as 0.276 (0.053, 0.498) to 0.475 (0.103, 0.848) ng/mg increase of H3K9ac. In addition, every 1 more day exposure at high level of TRAP (in tunnel) also significantly changed the levels of DNA methylation (ranging from −0.842% to 0.248%) and H3K9ac (16.033 and 15.718 ng/mg pro in PBMC and lung tissue, respectively) changes. Season and/or sex could interact with air pollutants in affecting DNA methylation and H3K9ac. The findings showed that TRAP exposure is dose- and time- dependently associated with the changes of DNA methylation and H3K9ac.

Genetic Variants in the Bone Morphogenic Protein Gene Family Modify the Association between Residential Exposure to Traffic and Peripheral Arterial Disease

There is a growing literature indicating that genetic variants modify many of the associations between environmental exposures and clinical outcomes, potentially by increasing susceptibility to these exposures. However, genome-scale investigations of these interactions have been rarely performed particularly in the case of air pollution exposures. We performed race-stratified genome-wide gene-environment interaction association studies on European-American (EA, N = 1623) and African-American (AA, N = 554) cohorts to investigate the joint influence of common single nucleotide polymorphisms (SNPs) and residential exposure to traffic (“traffic exposure”)—a recognized vascular disease risk factor—on peripheral arterial disease (PAD). Traffic exposure was estimated via the distance from the primary residence to the nearest major roadway, defined as the nearest limited access highways or major arterial. The rs755249-traffic exposure interaction was associated with PAD at a genome-wide significant level (P = 2.29x10^-8) in European-Americans. Rs755249 is located in the 3’ untranslated region of BMP8A, a member of the bone morphogenic protein (BMP) gene family. Further investigation revealed several variants in BMP genes associated with PAD via an interaction with traffic exposure in both the EA and AA cohorts; this included interactions with non-synonymous variants in BMP2, which is regulated by air pollution exposure. The BMP family of genes is linked to vascular growth and calcification and is a novel gene family for the study of PAD pathophysiology. Further investigation of BMP8A using the Genotype Tissue Expression Database revealed multiple variants with nominally significant (P < 0.05) interaction P-values in our EA cohort were significant BMP8A eQTLs in tissue types highlight relevant for PAD such as rs755249 (tibial nerve, eQTL P = 3.6x10^-6) and rs1180341 (tibial artery, eQTL P = 5.3x10^-6). Together these results reveal a novel gene, and possibly gene family, associated with PAD via an interaction with traffic air pollution exposure. These results also highlight the potential for interactions studies, particularly at the genome scale, to reveal novel biology linking environmental exposures to clinical outcomes.

Characteristics of DNA methylation changes induced by traffic-related air pollution

Traffic-related air pollution (TRAP) is a potential risk factor for numerous respiratory disorders, including lung cancer, while alteration of DNA methylation may be one of the underlying mechanisms. However, the effects of TRAP mixtures on DNA methylation have not been investigated. We have studied the effects of brief or prolonged TRAP exposures on DNA methylation in the rat. The exposures were performed in spring and autumn, with identical study procedures. In each season, healthy Wistar rats were exposed to TRAP at for 4 h, 7 d, 14 d, or 28 d. Global DNA methylation (LINE-1 and Alu) and specific gene methylation (p16(CDKN2A), APC, and iNOS) in the DNA from blood and lung tissues were quantified by pyrosequencing. Multiple linear regression was applied to assess the influence of air pollutants on DNA methylation levels. The levels of PM2.5, PM10, and NO2 in the high and moderate groups were significantly higher than in the control group. The DNA methylation levels were not significantly different between spring and autumn. When spring and autumn data were analyzed together, PM2.5, PM10, and NO2 exposures were associated with changes in%5mC (95% CI) in LINE-1, iNOS, p16(CDKN2A), and APC ranging from -0.088 (-0.150, -0.026) to 0.102 (0.049, 0.154) per 1 μg/m(3) increase in the pollutant concentration. Prolonged exposure to a high level of TRAP was negatively associated with LINE-1 and iNOS methylation, and positively associated with APC methylations in the DNA from lung tissues but not blood. These findings show that TRAP exposure is associated with decreased methylation of LINE-1 and iNOS, and increased methylation of p16(CDKN2A) and APC.

Exposure assessment in cohort studies of childhood asthma

BACKGROUND

The environment is suspected to play an important role in the development of childhood asthma. Cohort studies are a powerful observational design for studying exposure-response relationships, but their power depends in part upon the accuracy of the exposure assessment.

OBJECTIVE

The purpose of this paper is to summarize and discuss issues that make accurate exposure assessment a challenge and to suggest strategies for improving exposure assessment in longitudinal cohort studies of childhood asthma and allergies.

DATA SYNTHESIS

Exposures of interest need to be prioritized, because a single study cannot measure all potentially relevant exposures. Hypotheses need to be based on proposed mechanisms, critical time windows for effects, prior knowledge of physical, physiologic, and immunologic development, as well as genetic pathways potentially influenced by the exposures. Modifiable exposures are most important from the public health perspective. Given the interest in evaluating gene-environment interactions, large cohort sizes are required, and planning for data pooling across independent studies is critical. Collection of additional samples, possibly through subject participation, will permit secondary analyses. Models combining air quality, environmental, and dose data provide exposure estimates across large cohorts but can still be improved.

CONCLUSIONS

Exposure is best characterized through a combination of information sources. Improving exposure assessment is critical for reducing measurement error and increasing power, which increase confidence in characterization of children at risk, leading to improved health outcomes.

Prenatal environmental exposures, epigenetics, and disease

This review summarizes recent evidence that prenatal exposure to diverse environmental chemicals dysregulates the fetal epigenome, with potential consequences for subsequent developmental disorders and disease manifesting in childhood, over the lifecourse, or even transgenerationally. The primordial germ cells, embryo, and fetus are highly susceptible to epigenetic dysregulation by environmental chemicals, which can thereby exert multiple adverse effects. The data reviewed here on environmental contaminants have potential implications for risk assessment although more data are needed on individual susceptibility to epigenetic alterations and their persistence before this information can be used in formal risk assessments. The findings discussed indicate that identification of environmental chemicals that dysregulate the prenatal epigenome should be a priority in health research and disease prevention.

Environmental epigenetics and allergic diseases: recent advances

Significant strides in the understanding of the role of epigenetic regulation in asthma and allergy using both epidemiological approaches as well as experimental ones have been made. This review focuses on new research within the last 2 years. These include advances in determining how environmental agents implicated in airway disease can induce epigenetic changes, how epigenetic regulation can influence T helper cell differentiation and T regulatory cell production, and new discoveries of epigenetic regulation associated with clinical outcomes.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.