Epigenetic effects of shiftwork on blood DNA methylation

A Narrative Review of the Carcinogenic Effect of Night Shift and the Potential Protective Role of Melatonin

Since the IARC (International Agency for Research on Cancer) announcement in 2007 indicating the possibility of night-shift work carrying carcinogenesis risk, multiple studies on a global level have been conducted to investigate the correlation between night-shift work and cancer development. Circadian rhythm disruption and decreased melatonin production have been postulated as potential contributing factors. There is also growing evidence that night-shift workers tend to adopt unhealthier lifestyles which contribute to poorer health and increase the risk of developing diseases such as cancer. No experimental study has been specifically dedicated to testing specific methods that could decrease cancer risk in night-shift workers. While there are a few studies that investigate melatonin's concurrent use with chemotherapy in cancer patients, there is yet to be seen for studies that investigate melatonin specifically as a cancer prevention method. This narrative review aims to examine current evidence of healthcare night-shift work's risk in cancer incidence, potential pathogenesis, and its significance in clinical practice.

Chrono-Nutrition: Circadian Rhythm and Personalized Nutrition

The human circadian system has a period of approximately 24 h and studies on the consequences of "chornodisruption" have greatly expanded. Lifestyle and environmental factors of modern societies (i.e., artificial lighting, jetlag, shift work, and around-the-clock access to energy-dense food) can induce disruptions of the circadian system and thereby adversely affect individual health. Growing evidence demonstrates a complex reciprocal relationship between metabolism and the circadian system, in which perturbations in one system affect the other one. From a nutritional genomics perspective, genetic variants in clock genes can both influence metabolic health and modify the individual response to diet. Moreover, an interplay between the circadian rhythm, gut microbiome, and epigenome has been demonstrated, with the diet in turn able to modulate this complex link suggesting a remarkable plasticity of the underlying mechanisms. In this view, the study of the impact of the timing of eating by matching elements from nutritional research with chrono-biology, that is, chrono-nutrition, could have significant implications for personalized nutrition in terms of reducing the prevalence and burden of chronic diseases. This review provides an overview of the current evidence on the interactions between the circadian system and nutrition, highlighting how this link could in turn influence the epigenome and microbiome. In addition, possible nutritional strategies to manage circadian-aligned feeding are suggested.

Association between night shift work and methylation of a subset of immune-related genes

Introduction

Night shift (NS) work has been associated with an increased risk of different conditions characterized by altered inflammatory and immune responses, such as cardio-metabolic and infectious diseases, cancer, and obesity. Epigenetic modifications, such as DNA methylation, might mirror alterations in biological processes that are influenced by NS work.

Methods

The present study was conducted on 94 healthy female workers with different working schedules and aimed at identifying whether NS was associated with plasmatic concentrations of the inflammatory proteins NLRP3 and TNF-alpha, as well as with DNA methylation levels of ten human endogenous retroviral (HERV) sequences, and nine genes selected for their role in immune and inflammatory processes. We also explored the possible role of the body mass index (BMI) as an additional susceptibility factor that might influence the effects of NS work on the tested epigenetic modifications.

Results and discussion

We observed a positive association between NS and NLRP3 levels (p-value 0.0379). Moreover, NS workers retained different methylation levels for ERVFRD-1 (p-value = 0.0274), HERV-L (p-value = 0.0377), and HERV-P (p-value = 0.0140) elements, and for BIRC2 (p-value = 0.0460), FLRT3 (p-value = 0.0422), MIG6 (p-value = 0.0085), and SIRT1 (p-value = 0.0497) genes. We also observed that the BMI modified the relationship between NS and the methylation of ERVE, HERV-L, and ERVW-1 elements. Overall, our results suggest that HERV methylation could pose as a promising biomolecular sensor to monitor not only the effect of NS work but also the cumulative effect of multiple stressors.

Circadian mechanism disruption is associated with dysregulation of inflammatory and immune responses: a systematic review

The circadian rhythms are regulated by the circadian clock which is under the control of suprachiasmatic nucleus of hypothalamus. The central and peripheral clocks on different tissue together synchronize to form circadian system. Factors disrupt the circadian rhythm, such as irregular eating patterns, sleep/wake time, night shift work and temperature. Due to the misalignment of central clock components, it has been recognized as the pathophysiology of lifestyle-related diseases mediated by the inflammation such as diabetes, obesity, neurological disorder and hormonal imbalance. Also we discuss the therapeutic effect of time-restricted feeding over diabetes and obesity caused by miscommunication between central and peripheral clock. The genetic and epigenetic changes involve due to the deregulation of circadian system. The aim of the present review is to discuss the circadian mechanisms that are involved in the complex interaction between host and external factors and its disruption is associated with deregulation of inflammatory and immune responses. Hence, we need to understand the mechanism of functioning of our biological clocks so that it helps us treat health-related problems such as jet lags, sleep disorders due to night-time shift work, obesity and mental disturbances. We hope minimal cost behavioural and lifestyle changes can improve circadian rhythms and presumably provide a better health.

Neighborhood characteristics and breast tumor methylation: using epigenomics to explore cancer outcome disparities

BACKGROUND

Social exposures may drive epigenetic alterations that affect racial disparities in breast cancer outcomes. This study examined the association between neighborhood-level factors and DNA methylation in non-Hispanic Black and White women diagnosed with breast cancer.

METHODS

Genome-wide DNA methylation was measured using the EPIC array in the tumor tissue of 96 women. Linear regression models were used to examine the association between nine neighborhood-level factors and methylation, regressing β values for each cytosine-phosphate guanine dinucleotide (CpG) site on neighborhood-level factors while adjusting for covariates. Neighborhood data were obtained from the Opportunity Atlas. We used a false discovery rate (FDR) threshold < 0.05, and for CpGs below this threshold, we examined interactions with race. We employed multivariable Cox proportional-hazards models to estimate whether aberrant methylation was associated with all-cause mortality.

RESULTS

26 of the CpG sites were associated with job density or college education (FDR < 0.05). Further exploration of these 26 CpG sites revealed no interactions by race, but a single probe in TMEM204 was associated with all-cause mortality.

CONCLUSION

We identified novel associations between neighborhood-level factors and the breast tumor DNA methylome. Our data are the first to show that dysregulation in neighborhood associated CpG sites may be associated with all-cause mortality. Neighborhood-level factors may contribute to differential tumor methylation in genes related to tumor progression and metastasis. This contributes to the increasing body of evidence that area-level factors (such as neighborhood characteristics) may play an important role in cancer disparities through modulation of the breast tumor epigenome.

Maternal anxiety and depression in pregnancy and DNA methylation of the NR3C1 glucocorticoid receptor gene

Aim: To quantify associations of anxiety and depression during pregnancy with differential cord blood DNA methylation of the glucorticoid receptor ( NR3C1). Materials & methods: Pregnancy anxiety, trait anxiety and depressive symptoms were collected using the Pregnancy Related Anxiety Scale, State-Trait Anxiety Index and Edinburgh Postnatal Depression Scale, respectively. NR3C1 methylation was determined at four methylation sites. Results: DNA methylation of CpG 1 in the NR3C1 CpG island shore was higher in infants born to women with high pregnancy anxiety (β 2.54, 95% CI: 0.49–4.58) and trait anxiety (β 1.68, 95% CI: 0.14–3.22). No significant association was found between depressive symptoms and NR3C1 methylation. Conclusion: We found that maternal anxiety was associated with increased NR3C1 CpG island shore methylation.

Shift work, DNA methylation and epigenetic age

BACKGROUND

Shift work has been associated with increased risk of age-related morbidity and mortality. Biological age, estimated using DNA methylation (DNAm), may quantify the biological consequences of shift work on the risk of age-related disease. We examined whether prior employment in shift-working occupations was associated with epigenetic age acceleration.

METHODS

In a sample of non-Hispanic White women aged 35-74 (n = 2574), we measured DNAm using the Illumina Infinium Human450 BeadChip and calculated DNAm age using three established epigenetic clocks. Age-acceleration metrics were derived by regressing DNAm age on chronological age and predicting the residuals. Using linear regression, we estimated associations between shift work history and age acceleration. We also conducted an epigenome-wide association study using robust linear-regression models corrected with false discovery rate (FDR) q-values.

RESULTS

Approximately 7% of women reported any shift work. Higher age acceleration was observed for a 1-year increase in overall [β = 0.11, 95% confidence interval (CI): 0.02-0.21] and night-specific shift work (β = 0.12, 95% CI: 0.03-0.21). The association was strongest for ≥10 years of night shift work (β = 3.16, 95% CI: 1.17-5.15). From the epigenome-wide association study, years of overall and night shift work were associated with DNAm at 66 and 85 CpG sites (FDR < 0.05), respectively. Years of night shift work was associated with lower methylation of a CpG in the gene body of ZFHX3 (cg04994202, q = 0.04), a gene related to circadian rhythm.

CONCLUSIONS

Shift work was associated with differential CpG site methylation and with differential DNAm patterns, measured by epigenetic age acceleration, consistent with long-term negative health effects.

Night Shift Work, DNA Methylation and Telomere Length: An Investigation on Hospital Female Nurses

Increased breast cancer risk has been reported in some night shift (NS) workers but underlying biological mechanisms are still unclear. We assessed the association between NS work and DNA methylation of tumor suppressor (TP53, CDKN2A, BRCA1, BRCA2) and estrogen receptor (ESR1, ESR2) genes, methylation of repetitive elements (LINE-1, Alu), and telomere length (TL). Forty six female nurses employed in NS for at least two years were matched by age (30–45 years) and length of service (≥1 year) with 51 female colleagues not working in NS. Each subject underwent a semi-structured interview and gave a blood sample. We applied linear regression and spline models adjusted for age, BMI, smoking habit, oral contraceptive use, parity and marital status/age at marriage. Currently working in NS was associated with ESR1 hypomethylation (β: −1.85 (95%CI: −3.03; −0.67), p = 0.003). In current and former NS workers we observed TP53 (−0.93 (−1.73; −0.12), p = 0.03) and BRCA1 (−1.14 (−1.71; −0.58), p <0.001) hypomethylation. We found an increase between TL and number of years in NS in subjects employed in NS <12 years (0.06 (0.03; 0.09), p <0.001), while a decrease if employed in NS ≥12 years (−0.07 −0.10; −0.04), p <0.001). Our findings show NS-associated markers potentially involved in cellular aging, genomic instability, and cancer development.

DNA methylation among firefighters

Firefighters are exposed to carcinogens and have elevated cancer rates. We hypothesized that occupational exposures in firefighters would lead to DNA methylation changes associated with activation of cancer pathways and increased cancer risk. To address this hypothesis, we collected peripheral blood samples from 45 incumbent and 41 new recruit non-smoking male firefighters and analyzed the samples for DNA methylation using an Illumina Methylation EPIC 850k chip. Adjusting for age and ethnicity, we performed: 1) genome-wide differential methylation analysis; 2) genome-wide prediction for firefighter status (incumbent or new recruit) and years of service; and 3) Ingenuity Pathway Analysis (IPA). Four CpGs, including three in the YIPF6, MPST, and PCED1B genes, demonstrated above 1.5-fold statistically significant differential methylation after Bonferroni correction. Genome-wide methylation predicted with high accuracy incumbent and new recruit status as well as years of service among incumbent firefighters. Using IPA, the top pathways with more than 5 gene members annotated from differentially methylated probes included Sirtuin signaling pathway, p53 signaling, and 5' AMP-activated protein kinase (AMPK) signaling. These DNA methylation findings suggest potential cellular mechanisms associated with increased cancer risk in firefighters.

Association of Serotonin Transporter Gene AluJb Methylation with Major Depression, Amygdala Responsiveness, 5-HTTLPR/rs25531 Polymorphism, and Stress

DNA methylation profiles of the serotonin transporter gene (SLC6A4) have been shown to alter SLC6A4 expression, drive antidepressant treatment response and modify brain functions. This study investigated whether methylation of an AluJb element in the SLC6A4 promotor was associated with major depressive disorder (MDD), amygdala reactivity to emotional faces, 5-HTTLPR/rs25531 polymorphism, and recent stress. MDD patients (n=122) and healthy controls (HC, n=176) underwent fMRI during an emotional face-matching task. Individual SLC6A4 AluJb methylation profiles were ascertained and associated with MDD, amygdala reactivity, 5-HTTLPR/rs25531, and stress. SLC6A4 AluJb methylation was significantly lower in MDD compared to HC and in stressed compared to less stressed participants. Lower AluJb methylation was particularly found in 5-HTTLPR/rs25531 risk allele carriers under stress and correlated with less depressive episodes. fMRI analysis revealed a significant interaction of AluJb methylation and diagnosis in the amygdala, with MDD patients showing lower AluJb methylation associated with decreased amygdala reactivity. While no joint effect of AluJb methylation and 5-HTTLPR/rs25531 existed, risk allele carriers showed significantly increased bilateral amygdala activation. These findings suggest a role of SLC6A4 AluJb methylation in MDD, amygdala reactivity, and stress reaction, partly interwoven with 5-HTTLPR/rs25531 effects. Patients with low methylation in conjunction with a shorter MDD history and decreased amygdala reactivity might feature a more stress-adaptive epigenetic process, maybe via theoretically possible endogenous antidepressant-like effects. In contrast, patients with higher methylation might possibly suffer from impaired epigenetic adaption to chronic stress. Further, the 5-HTTLPR/rs25531 association with amygdala activation was confirmed in our large sample.

Circadian gene methylation in rotating-shift nurses: a cross-sectional study

Investigating the methylation status of the circadian genes may contribute to a better understanding of the shift work-related circadian disruption in individuals exposed to artificial light at night. In the present study, we determined the methylation status of the circadian genes associated with a shift work pattern among nurses and midwives participating in a cross-sectional study in Lodz, Poland. Quantitative methylation polymerase chain reaction assays were used to assess promoter CpG methylation in PER1, PER2, PER3, CRY1, CRY2, BMAL1, CLOCK, and NPAS2 in genomic DNA from whole blood of 347 women having a rotating-shift work schedule and 363 women working days only. The percentage of methylated reference (PMR) was assessed using fluorescent probes for PER1, PER2, PER3, CRY1, and NPAS2, and the percentage of gene methylation, as the methylation index (MI), using two sets of primers for BMAL1, CLOCK, and CRY2. We tested the possible association between current and lifetime rotating night-shift work characteristics and circadian gene methylation by using proportional odds regression model with blood DNA methylation, categorized into tertiles, and adjusted for age, current smoking status, folate intake and blood collection time. The findings indicated that CpG methylation in PER2 promoter was significantly decreased (P < 0.004) among nurses and midwives currently working rotating shifts, as compared with day-working nurses and midwives. The lower percentage of PER2 methylation was associated with a higher monthly frequency of current night duties (2-7 night shifts, and eight or more night shifts per month) (P = 0.012) and was associated at borderline significance (P = 0.092) with the lifetime duration of shift work (>10 ≤ 20 years and >20 ≤ 43 years of rotating-shift work) among nurses and midwives (N = 710). Moreover, women with a longer lifetime duration of shift work presented a lower status of PER1 methylation (P = 0.040) than did the women with up to 10 years of rotating-shift work. Long lifetime duration of shift work (> 10 years) among current rotating night-shift workers (N =  347) was associated with BMAL1 hypomethylation (P = 0.013). Among eight of the investigated circadian genes, only PER1, PER2, and BMAL1 showed differential methylation attributable to the rotating-shift work of nurses and midwives. The findings on blood-based DNA methylation in the circadian genes may provide a better insight into the mechanistic principles underlying the possible health effects of night-shift work but these should be verified in further studies recruiting larger populations of shift workers.

Sleep quality and methylation status of selected tumor suppressor genes among nurses and midwives

Chronic sleep restriction may affect metabolism, hormone secretion patterns and inflammatory responses. Limited reports suggest also epigenetic effects, such as changes in DNA methylation profiles. The study aims to assess the potential association between poor sleep quality or sleep duration and the levels of 5-methylcytosine in the promoter regions of selected tumor suppressor genes. A cross-sectional study was conducted on 710 nurses and midwives aged 40-60 years. Data from interviews regarding sleep habits and potential confounders were used. The methylation status of tumor suppressor genes was determined via qMSP reactions using DNA samples derived from leucocytes. No significant findings were observed in the total study population or in the two subgroups of women stratified by the current system of work. A borderline significance association was observed between a shorter duration of sleep and an increased methylation level in CDKN2A among day working nurses and midwives. Further studies are warranted to explore this under-investigated topic.

Sleep quality and methylation status of core circadian rhythm genes among nurses and midwives

ABSTARCT Poor sleep quality or sleep restriction is associated with sleepiness and concentration problems. Moreover, chronic sleep restriction may affect metabolism, hormone secretion patterns and inflammatory responses. Limited recent reports suggest a potential link between sleep deprivation and epigenetic effects such as changes in DNA methylation profiles. The aim of the present study was to assess the potential association between poor sleep quality or sleep duration and the levels of 5-methylcytosine in the promoter regions of PER1, PER2, PER3, BMAL1, CLOCK, CRY1 CRY2 and NPAS2 genes, taking into account rotating night work and chronotype as potential confounders or modifiers. A cross-sectional study was conducted on 710 nurses and midwives (347 working on rotating nights and 363 working only during the day) aged 40-60 years. Data from in-person interviews about sleep quality, chronotype and potential confounders were used. Sleep quality and chronotype were assessed using Pittsburgh Sleep Quality Questionnaire (PSQI) and Morningness-Eveningness Questionnaire (MEQ), respectively. Morning blood samples were collected. The methylation status of the circadian rhythm genes was determined via quantitative methylation-specific real-time PCR assays (qMSP) reactions using DNA samples derived from leucocytes. The proportional odds regression model was fitted to quantify the relationship between methylation index (MI) as the dependent variable and sleep quality or sleep duration as the explanatory variable. Analyses were carried out for the total population as well as for subgroups of women stratified by the current system of work (rotating night shift/day work) and chronotype (morning type/intermediate type/evening type). A potential modifying effect of the system of work or the chronotype was examined using the likelihood ratio test. No significant findings were observed in the total study population. Subgroup analyses revealed two statistically significant associations between a shorter sleep duration and 1) methylation level in PER2 among day workers, especially those with the morning chronotype (OR = 2.31, 95%CI:1.24-4.33), and 2) methylation level in CRY2 among subjects with the intermediate chronotype, particularly among day workers (OR = 0.52, 95%CI:0.28-0.96). The study results demonstrated a positive association between average sleep duration of less than 6 hours and the methylation level of PER2 among morning chronotype subjects, and an inverse association for CRY2 among intermediate chronotype subjects, but only among day workers. Both the system of work and the chronotype turned out to be important confounders and modifiers in a number of analyses, making it necessary to consider them as potential covariates in future research on sleep deficiency outcomes. Further studies are warranted to explore this under-investigated topic.

Rotating night work, lifestyle factors, obesity and promoter methylation in BRCA1 and BRCA2 genes among nurses and midwives

Some recent evidence suggests that environmental and lifestyle factors may modify DNA methylation. We hypothesized that rotating night work and several modifiable factors may be associated with the methylation of the promoter regions within two tumor suppressor and DNA repair genes: BRCA1 and BRCA2. The methylation status of BRCA1 and BRCA2 was determined via qMSP reactions using DNA samples derived from blood leucocytes of 347 nurses and midwives working rotating nights and 363 working during the days. The subjects were classified into unmethylated vs methylated BRCA1 and BRCA2 when the methylation index was 0% or >0%, respectively. The adjusted odds ratios with 95% confidence intervals were calculated for night work status, smoking, obesity, physical activity and alcohol drinking. Current night shift work or night work history was not associated with methylation status of the promoter sites within BRCA1 and BRCA2 genes. We observed weak associations between smoking and the methylation status of BRCA1 with OR = 1.50 (95%CI: 0.98–2.29) for current smoking, OR = 1.83, 95CI: 1.08–3.13 for smoking longer than 31 years, and 0.1>p>0.05 for trends for the number of cigarettes per day, smoking duration and packyears. In conclusion, no links between night shift work and methylation of the promoter region within the BRCA1, and BRCA2 genes were observed in this exploratory analysis. The findings of our study weakly support the hypothesis that smoking may contribute to epigenetic events.

Case-control study of candidate gene methylation and adenomatous polyp formation

PURPOSE

Colorectal cancer (CRC) is one of the most common and preventable forms of cancer but remains the second leading cause of cancer-related death. Colorectal adenomas are precursor lesions that develop in 70-90 % of CRC cases. Identification of peripheral biomarkers for adenomas would help to enhance screening efforts. This exploratory study examined the methylation status of 20 candidate markers in peripheral blood leukocytes and their association with adenoma formation.

METHODS

Patients recruited from a local endoscopy clinic provided informed consent and completed an interview to ascertain demographic, lifestyle, and adenoma risk factors. Cases were individuals with a histopathologically confirmed adenoma, and controls included patients with a normal colonoscopy or those with histopathological findings not requiring heightened surveillance (normal biopsy, hyperplastic polyp). Methylation-specific polymerase chain reaction was used to characterize candidate gene promoter methylation. Odds ratios (ORs) and 95 % confidence intervals (95% CIs) were calculated using unconditional multivariable logistic regression to test the hypothesis that candidate gene methylation differed between cases and controls, after adjustment for confounders.

RESULTS

Complete data were available for 107 participants; 36 % had adenomas (men 40 %, women 31 %). Hypomethylation of the MINT1 locus (OR 5.3, 95% CI 1.0-28.2) and the PER1 (OR 2.9, 95% CI 1.1-7.7) and PER3 (OR 11.6, 95% CI 1.6-78.5) clock gene promoters was more common among adenoma cases. While specificity was moderate to high for the three markers (71-97 %), sensitivity was relatively low (18-45 %).

CONCLUSION

Follow-up of these epigenetic markers is suggested to further evaluate their utility for adenoma screening or surveillance.

Effects of environmental noise exposure on DNA methylation in the brain and metabolic health

Environmental noise exposure is associated with adverse effects on human health including hearing loss, heart disease, and changes in stress-related hormone levels. Alteration in DNA methylation in response to environmental exposures is a well-known phenomenon and it is implicated in many human diseases. Understanding how environmental noise exposures affect DNA methylation patterns may help to elucidate the link between noise and adverse effects on health. In this pilot study we examined the effects of environmental noise exposure on DNA methylation of genes related to brain function and investigated whether these changes are related with metabolic health. We exposed four groups of male Wistar rats to moderate intensity noise (70-75dB with 20-4000Hz) at night for three days as short-term exposure, and for three weeks as long-term exposure. Noise exposure was limited to 45dB during the daytime. Control groups were exposed to only 45dB, day and night. We measured DNA methylation in the Bdnf, Comt, Crhr1, Mc2r, and Snca genes in tissue from four brain regions of the rats (hippocampus, frontal lobe, medulla oblongata, and inferior colliculus). Further, we measured blood pressure and body weight after long-term noise exposure. We found that environmental noise exposure is associated with gene-specific DNA methylation changes in specific regions of the brain. Changes in DNA methylation are significantly associated with changes in body weight (between Bdnf DNA methylation and Δ body weight: r=0.59, p=0.018; and between LINE-1 ORF DNA methylation and Δ body weight: =-0.80, p=0.0004). We also observed that noise exposure decreased blood pressure (p=0.038 for SBP, p=0.017 for DBP and p 0. 017 for MAP) and decreased body weight (β=-26g, p=0.008). In conclusion, environmental noise exposures can induce changes in DNA methylation in the brain, which may be associated with adverse effects upon metabolic health through modulation of response to stress-related hormones.

Childhood abuse, promoter methylation of leukocyte NR3C1 and the potential modifying effect of emotional support

AIM

To investigate childhood abuse victimization in relation to adult DNA methylation levels in a novel region of NR3C1, with emotional support as a possible modifier.

MATERIALS & METHODS

295 participants from the Black Women's Health Study. Multivariable linear regression models were used to compute differences in mean percent methylation levels.

RESULTS

Women reporting childhood abuse victimization exhibited higher mean NR3C1 methylation levels than nonabused women, with a clear dose-response relationship. Childhood emotional support appeared to attenuate associations only among women with the highest levels of physical and sexual abuse.

CONCLUSION

NR3C1 mean methylation was higher among women who reported childhood abuse. Further research is warranted to clarify whether or the extent to which childhood emotional support buffers the association.

Epigenetic alterations in the suprachiasmatic nucleus and hippocampus contribute to age-related cognitive decline

Circadian rhythm dysfunction and cognitive decline, specifically memory loss, frequently accompany natural aging. Circadian rhythms and memory are intertwined, as circadian rhythms influence memory formation and recall in young and old rodents. Although, the precise relationship between circadian rhythms and memory is still largely unknown, it is hypothesized that circadian rhythm disruption, which occurs during aging, contributes to age-associated cognitive decline, specifically memory loss. While there are a variety of mechanisms that could mediate this effect, changes in the epigenome that occur during aging has been proposed as a potential candidate. Interestingly, epigenetic mechanisms, such as DNA methylation and sirtuin1 (SIRT1) are necessary for both circadian rhythms and memory. During aging, similar alterations of epigenetic mechanisms occur in the suprachiasmatic nucleus (SCN) and hippocampus, which are necessary for circadian rhythm generation and memory, respectively. Recently, circadian rhythms have been linked to epigenetic function in the hippocampus, as some of these epigenetic mechanisms oscillate in the hippocampus and are disrupted by clock gene deletion. The current paper will review how circadian rhythms and memory change with age, and will suggest how epigenetic changes in these processes might contribute to age-related cognitive decline.

Methylation on the Circadian Gene BMAL1 Is Associated with the Effects of a Weight Loss Intervention on Serum Lipid Levels

The circadian clock system has been linked to the onset and development of obesity and some accompanying comorbidities. Epigenetic mechanisms, such as DNA methylation, are putatively involved in the regulation of the circadian clock system. The aim of this study was to investigate the influence of a weight loss intervention based on an energy-controlled Mediterranean dietary pattern in the methylation levels of 3 clock genes, BMAL1, CLOCK, and NR1D1, and the association between the methylation levels and changes induced in the serum lipid profile with the weight loss treatment. The study sample enrolled 61 women (body mass index = 28.6 ± 3.4 kg/m(2); age: 42.2 ± 11.4 years), who followed a nutritional program based on a Mediterranean dietary pattern. DNA was isolated from whole blood obtained at the beginning and end point. Methylation levels at different CpG sites of BMAL1, CLOCK, and NR1D1 were analyzed by Sequenom's MassArray. The energy-restricted intervention modified the methylation levels of different CpG sites in BMAL1 (CpGs 5, 6, 7, 9, 11, and 18) and NR1D1 (CpGs 1, 10, 17, 18, 19, and 22). Changes in cytosine methylation in the CpG 5 to 9 region of BMAL1 with the intervention positively correlated with the eveningness profile (p = 0.019). The baseline methylation of the CpG 5 to 9 region in BMAL1 positively correlated with energy (p = 0.047) and carbohydrate (p = 0.017) intake and negatively correlated with the effect of the weight loss intervention on total cholesterol (p = 0.032) and low-density lipoprotein cholesterol (p = 0.005). Similar significant and positive correlations were found between changes in methylation levels in the CpG 5 to 9 region of BMAL1 due to the intervention and changes in serum lipids (p < 0.05). This research describes apparently for the first time an association between changes in the methylation of the BMAL1 gene with the intervention and the effects of a weight loss intervention on blood lipids levels.

Exposure to persistent organic pollutants and sperm DNA methylation changes in Arctic and European populations

Persistent organic pollutants (POPs), such as PCBs (polychlorinated biphenyls) and DDT [1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane], are environmental contaminants with potential endocrine disrupting activity. DNA methylation levels in peripheral blood lymphocytes have been associated with serum concentrations of POPs in Greenland Inuit and Korean populations. Greenland Inuits are characterized by the highest worldwide POP levels. In this cross-sectional study we evaluated the relationship between serum POP concentrations and DNA methylation levels in sperm of non-occupationally exposed fertile men from Greenland, Warsaw (Poland), and Kharkiv (Ukraine). Serum levels of PCB-153 [1,2,4-trichloro-5-(2,4,5-trichlorophenyl)benzene], as a proxy of the total PCBs body burden, and of p,p'-DDE [1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene], the main metabolite of DDT were measured. Sperm DNA methylation level was assessed globally by flow cytometric (FCM) immunodetection of 5-methyl-cytosines and at specific repetitive DNA sequences (Alu, LINE-1, Satα) by PCR-pyrosequencing after bisulfite conversion. Multivariate linear regression analysis was applied to investigate correlations between serum POP concentrations and DNA methylation. No consistent associations between exposure to POPs and sperm DNA methylation at repetitive DNA sequences were detected. A statistically significant global decrease in methylation was associated with exposure to either POP by FCM analysis. This is the first study to investigate environmental exposure to POPs and DNA methylation levels considering sperm as the target cells. Although POP exposure appears to have a limited negative impact on sperm DNA methylation levels in adult males, the global hypomethylation detected by one of the methods applied suggests that further investigation is warranted.

Performance of Different Analytical Software Packages in Quantification of DNA Methylation by Pyrosequencing

BACKGROUND

Pyrosequencing has emerged as an alternative method of nucleic acid sequencing, well suited for many applications which aim to characterize single nucleotide polymorphisms, mutations, microbial types and CpG methylation in the target DNA. The commercially available pyrosequencing systems can harbor two different types of software which allow analysis in AQ or CpG mode, respectively, both widely employed for DNA methylation analysis.

OBJECTIVE

Aim of the study was to assess the performance for DNA methylation analysis at CpG sites of the two pyrosequencing software which allow analysis in AQ or CpG mode, respectively. Despite CpG mode having been specifically generated for CpG methylation quantification, many investigations on this topic have been carried out with AQ mode. As proof of equivalent performance of the two software for this type of analysis is not available, the focus of this paper was to evaluate if the two modes currently used for CpG methylation assessment by pyrosequencing may give overlapping results.

METHODS

We compared the performance of the two software in quantifying DNA methylation in the promoter of selected genes (GSTP1, MGMT, LINE-1) by testing two case series which include DNA from paraffin embedded prostate cancer tissues (PC study, N = 36) and DNA from blood fractions of healthy people (DD study, N = 28), respectively.

RESULTS

We found discrepancy in the two pyrosequencing software-based quality assignment of DNA methylation assays. Compared to the software for analysis in the AQ mode, less permissive criteria are supported by the Pyro Q-CpG software, which enables analysis in CpG mode. CpG mode warns the operators about potential unsatisfactory performance of the assay and ensures a more accurate quantitative evaluation of DNA methylation at CpG sites.

CONCLUSION

The implementation of CpG mode is strongly advisable in order to improve the reliability of the methylation analysis results achievable by pyrosequencing.

Psychological factors and DNA methylation of genes related to immune/inflammatory system markers: the VA Normative Aging Study

OBJECTIVES

Although psychological factors have been associated with chronic diseases such as coronary heart disease (CHD), the underlying pathways for these associations have yet to be elucidated. DNA methylation has been posited as a mechanism linking psychological factors to CHD risk. In a cohort of community-dwelling elderly men, we explored the associations between positive and negative psychological factors with DNA methylation in promoter regions of multiple genes involved in immune/inflammatory processes related to atherosclerosis.

DESIGN

Prospective cohort study.

SETTING

Greater Boston, Massachusetts area.

PARTICIPANTS

Samples of 538 to 669 men participating in the Normative Aging Study cohort with psychological measures and DNA methylation measures, collected on 1-4 visits between 1999 and 2006 (mean age=72.7 years at first visit).

OUTCOME MEASURES

We examined anxiety, depression, hostility and life satisfaction as predictors of leucocyte gene-specific DNA methylation. We estimated repeated measures linear mixed models, controlling for age, smoking, education, history of heart disease, stroke or diabetes, % lymphocytes, % monocytes and plasma folate.

RESULTS

Psychological distress measured by anxiety, depression and hostility was positively associated, and happiness and life satisfaction were inversely associated with average Intercellular Adhesion Molecule-1 (ICAM-1) and coagulation factor III (F3) promoter methylation levels. There was some evidence that hostility was positively associated with toll-like receptor 2 (TLR-2) promoter methylation, and that life satisfaction was inversely associated with TLR-2 and inducible nitric oxide synthase (iNOS) promoter methylation. We observed less consistent and significant associations between psychological factors and average methylation for promoters of the genes for glucocorticoid receptor (NR3C1), interferon-γ (IFN-γ) and interleukin 6 (IL-6).

CONCLUSIONS

These findings suggest that positive and negative psychological factors affect DNA methylation of selected genes involved in chronic immune/inflammatory processes and inflammation-related endothelial dysfunction. Such epigenetic changes may represent biological pathways that mediate the effects of psychological factors on CHD.

Environmental Impact on DNA Methylation in the Germline: State of the Art and Gaps of Knowledge

The epigenome consists of chemical changes in DNA and chromatin that without modifying the DNA sequence modulate gene expression and cellular phenotype. The epigenome is highly plastic and reacts to changing external conditions with modifications that can be inherited to daughter cells and across generations. Whereas this innate plasticity allows for adaptation to a changing environment, it also implies the potential of epigenetic derailment leading to so-called epimutations. DNA methylation is the most studied epigenetic mark. DNA methylation changes have been associated with cancer, infertility, cardiovascular, respiratory, metabolic, immunologic, and neurodegenerative pathologies. Experiments in rodents demonstrate that exposure to a variety of chemical stressors, occurring during the prenatal or the adult life, may induce DNA methylation changes in germ cells, which may be transmitted across generations with phenotypic consequences. An increasing number of human biomonitoring studies show environmentally related DNA methylation changes mainly in blood leukocytes, whereas very few data have been so far collected on possible epigenetic changes induced in the germline, even by the analysis of easily accessible sperm. In this paper, we review the state of the art on factors impinging on DNA methylation in the germline, highlight gaps of knowledge, and propose priorities for future studies.

Epigenetics: Its Understanding Is Crucial to a Sustainable Healthcare System

Understanding the molecular impact of lifestyle factors has never been so important; a period in time where there are so many adults above retirement age has been previously unknown. As a species, our life expectancy is increasing yet the period of our lives where we enjoy good health is not expanding proportionately. Over the next 50 years we will need to almost double the percentage of GDP spent on health care, largely due to the increasing incidence of obesity related chronic diseases. A greater understanding and implementation of an integrated approach to health is required. Research exploring the impact of nutritional and exercise intervention on the epigenetically flexible genome is up front in terms of addressing healthy aging. Alongside this, we need a greater understanding of the interaction with our immune and nervous systems in preserving and maintaining health and cognition.

Genetics and epigenetics of circadian rhythms and their potential roles in neuropsychiatric disorders

Circadian rhythm alterations have been implicated in multiple neuropsychiatric disorders, particularly those of sleep, addiction, anxiety, and mood. Circadian rhythms are known to be maintained by a set of classic clock genes that form complex mutual and self-regulatory loops. While many other genes showing rhythmic expression have been identified by genome-wide studies, their roles in circadian regulation remain largely unknown. In attempts to directly connect circadian rhythms with neuropsychiatric disorders, genetic studies have identified gene mutations associated with several rare sleep disorders or sleep-related traits. Other than that, genetic studies of circadian genes in psychiatric disorders have had limited success. As an important mediator of environmental factors and regulators of circadian rhythms, the epigenetic system may hold the key to the etiology or pathology of psychiatric disorders, their subtypes or endophenotypes. Epigenomic regulation of the circadian system and the related changes have not been thoroughly explored in the context of neuropsychiatric disorders. We argue for systematic investigation of the circadian system, particularly epigenetic regulation, and its involvement in neuropsychiatric disorders to improve our understanding of human behavior and disease etiology.

Clinical implications of interferon-γ genetic and epigenetic variants

Interferon-γ (IFN-γ) is an integral and critical molecule of the immune system, with multiple functions, mostly related to the T helper type 1 (Th1) response to infection. It is critical for defence against mycobacterial infection and is of increasing interest in defence against fungi. In this article, we review the genetic and epigenetic variants affecting IFN-γ expression and investigate its role in disease, with an emphasis on fungal diseases such as invasive and chronic pulmonary aspergillosis. Over 347 IFN-γ gene variants have been described, in multiple ethnic populations. Many appear to confer a susceptibility to disease, especially tuberculosis (TB) and hepatitis, but also some non-infectious conditions such as aplastic anaemia, cervical cancer and psoriasis. Several epigenetic modifications are also described, increasing IFN-γ expression in Th1 lymphocytes and reducing IFN-γ expression in Th2 lymphocytes. Recombinant IFN-γ administration is licensed for the prophylaxis of infection (bacterial and fungal) in patients with the phagocyte functional deficiency syndrome chronic granulomatous disease, although the benefits appear limited. Interferon-γ therapy is given to patients with profound defects in IFN-γ and interleukin-12 production and appears to be beneficial for patients with invasive aspergillosis and cryptococcal meningitis, but the studies are not definitive. A high proportion of patients with chronic pulmonary aspergillosis are poor producers of IFN-γ in response to multiple stimuli and could also benefit from IFN-γ administration. The investigation and management of patients with possible or demonstrated IFN-γ deficiency in adulthood is poorly studied and could be greatly enhanced with the integration of genetic data.

Epigenetic regulation in biopsychosocial pathways

Theory and empirical evidence suggest that psychological stress and other adverse psychosocial experiences can contribute to cancer progression. Research has begun to explore the potential role of epigenetic changes in these pathways. In basic, animal and human models, exposure to stressors or to the products of the physiological stress response (e.g., cortisol) has been associated with epigenetic changes, such as DNA methylation and microRNA (miR) expression, which may influence tumor growth, progression, metastasis, or chemoresistance. However, the specific biological pathways linking stress, epigenetic changes, and cancer outcomes remain unclear. Numerous opportunities exist to extend the preliminary evidence for the role of epigenetic mechanisms in the biopsychosocial pathways contributing to cancer progression. Such work will improve our understanding of how the psychosocial environment influences cancer risk and survival, potentially leading to improved prevention and treatment strategies.

Epigenetics: relevance and implications for public health

Improved understanding of the multilayer regulation of the human genome has led to a greater appreciation of environmental, nutritional, and epigenetic risk factors for human disease. Chromatin remodeling, histone tail modifications, and DNA methylation are dynamic epigenetic changes responsive to external stimuli. Careful interpretation can provide insights for actionable public health through collaboration between population and basic scientists and through integration of multiple data sources. We review key findings in environmental epigenetics both in human population studies and in animal models, and discuss the implications of these results for risk assessment and public health protection. To ultimately succeed in identifying epigenetic mechanisms leading to complex phenotypes and disease, researchers must integrate the various animal models, human clinical approaches, and human population approaches while paying attention to life-stage sensitivity, to generate effective prescriptions for human health evaluation and disease prevention.

Nightshift work and genome-wide DNA methylation

The negative health effects of shift work, including carcinogenesis, may be mediated by changes in DNA methylation, particularly in the circadian genes. Using the Infinium HumanMethylation450 Bead Array (Illumina, San Diego, CA), we compared genome-wide methylation between 65 actively working dayshift workers and 59 actively working nightshift workers in the healthcare industry. A total of 473 800 loci, including 391 loci across the 12 core circadian genes, were analyzed to identify methylation markers associated with shift work status using linear regression models adjusted for gender, age, body mass index, race, smoking status and leukocyte cell profile as measured by flow cytometry. Analyses at the level of gene, CpG island and gene region were also conducted. To account for multiple comparisons, we controlled the false discovery rate (FDR ≤0.05). Significant differences between nightshift and dayshift workers were found at 16 135 of 473 800 loci, across 3769 of 20 164 genes, across 7173 of 22 721 CpG islands and across 5508 of 51 843 gene regions. For each significant loci, gene, CpG island or gene region, average methylation was consistently found to be decreased among nightshift workers compared to dayshift workers. Twenty-one loci located in the circadian genes were also found to be significantly hypomethylated among nightshift workers. The largest differences were observed for three loci located in the gene body of PER3. A total of nine significant loci were found in the CSNK1E gene, most of which were located in a CpG island and near the transcription start site of the gene. Methylation changes in these circadian genes may lead to altered expression of these genes which has been associated with cancer in previous studies. Gene ontology enrichment analysis revealed that among the significantly hypomethylated genes, processes related to host defense and immunity were represented. Our results indicate that the health effects of shift work may be mediated by hypomethylation of a wide variety of genes, including those related to circadian rhythms. While these findings need to be followed-up among a considerably expanded group of shift workers, the data generated by this study supports the need for future targeted research into the potential impacts of shift work on specific carcinogenic mechanisms.

Exposure to perfluoroalkyl substances and sperm DNA global methylation in Arctic and European populations

Perfluoroalkyl substances (PFASs) are widely used in a variety of industrial processes and products, and have been detected globally in humans and wildlife. PFASs are suspected to interfere with endocrine signaling and to adversely affect human reproductive health. The aim of the present study was to investigate the associations between exposure to PFASs and sperm global methylation levels in a population of non-occupationally exposed fertile men. Measurements of PFASs in serum from 262 partners of pregnant women from Greenland, Poland and Ukraine, were also carried out by liquid chromatography tandem mass spectrometry. Perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorohexane sulfonic acid (PFHxS), and perfluorononanoic acid (PFNA) were detected in 97% of the blood samples. Two surrogate markers were used to assess DNA global methylation levels in semen samples from the same men: (a) average DNA methylation level in repetitive DNA sequences (Alu, LINE-1, Satα) quantified by PCR-pyrosequencing after bisulfite conversion; (b) flow cytometric immunodetection of 5-methyl-cytosines. After multivariate linear regression analysis, no major consistent associations between PFASs exposure and sperm DNA global methylation endpoints could be detected. However, since weak but statistically significant associations of different PFASs with DNA hypo- and hyper-methylation were found in some of the studied populations, effects of PFASs on sperm epigenetic processes cannot be completely excluded, and this issue warrants further investigation.

Epigenetics of sleep and chronobiology

The circadian clock choreographs fundamental biological rhythms. This system is comprised of the master circadian pacemaker in the suprachiasmatic nucleus and associated pacemakers in other tissues that coordinate complex physiological processes and behaviors, such as sleep, feeding, and metabolism. The molecular circuitry that underlies these clocks and orchestrates circadian gene expression has been the focus of intensive investigation, and it is becoming clear that epigenetic factors are highly integrated into these networks. In this review, we draw attention to the fundamental roles played by epigenetic mechanisms in transcriptional and post-transcriptional regulation within the circadian clock system. We also highlight how alterations in epigenetic factors and mechanisms are being linked with sleep-wake disorders. These observations provide important insights into the pathogenesis and potential treatment of these disorders and implicate epigenetic deregulation in the significant but poorly understood interconnections now emerging between circadian processes and neurodegeneration, metabolic diseases, cancer, and aging.

Epigenetics in adipose tissue, obesity, weight loss, and diabetes

Given the role that diet and other environmental factors play in the development of obesity and type 2 diabetes, the implication of different epigenetic processes is being investigated. Although it is well known that external factors can cause cell type-dependent epigenetic changes, including DNA methylation, histone tail modifications, and chromatin remodeling, the regulation of these processes, the magnitude of the changes and the cell types in which they occur, the individuals more predisposed, and the more crucial stages of life remain to be elucidated. There is evidence that obese and diabetic people have a pattern of epigenetic marks different from nonobese and nondiabetic individuals. The main long-term goals in this field are the identification and understanding of the role of epigenetic marks that could be used as early predictors of metabolic risk and the development of drugs or diet-related treatments able to delay these epigenetic changes and even reverse them. But weight gain and insulin resistance/diabetes are influenced not only by epigenetic factors; different epigenetic biomarkers have also been identified as early predictors of weight loss and the maintenance of body weight after weight loss. The characterization of all the factors that are able to modify the epigenetic signatures and the determination of their real importance are hindered by the following factors: the magnitude of change produced by dietary and environmental factors is small and cumulative; there are great differences among cell types; and there are many factors involved, including age, with multiple interactions between them.

Methylation alterations at imprinted genes detected among long-term shiftworkers

Exposure to light at night through shiftwork has been linked to alterations in DNA methylation and increased risk of cancer development. Using an Illumina Infinium Methylation Assay, we analyzed methylation levels of 397 CpG sites in the promoter regions of 56 normally imprinted genes to investigate whether shiftwork is associated with alteration of methylation patterns. Methylation was significantly higher at 20 CpG sites and significantly lower at 30 CpG sites (P < 0.05) in 10 female long-term shiftworkers as compared to 10 female age- and folate intake-matched day workers. The strongest evidence for altered methylation patterns in shiftworkers was observed for DLX5, IGF2AS, and TP73 based on the magnitude of methylation change and consistency in the direction of change across multiple CpG sites, and consistent results were observed using quantitative DNA methylation analysis. We conclude that long-term shiftwork may alter methylation patterns at imprinted genes, which may be an important mechanism by which shiftwork has carcinogenic potential and warrants further investigation.

Opportunities and challenges for selected emerging technologies in cancer epidemiology: mitochondrial, epigenomic, metabolomic, and telomerase profiling

Remarkable progress has been made in the last decade in new methods for biologic measurements using sophisticated technologies that go beyond the established genome, proteome, and gene expression platforms. These methods and technologies create opportunities to enhance cancer epidemiologic studies. In this article, we describe several emerging technologies and evaluate their potential in epidemiologic studies. We review the background, assays, methods, and challenges and offer examples of the use of mitochondrial DNA and copy number assessments, epigenomic profiling (including methylation, histone modification, miRNAs, and chromatin condensation), metabolite profiling (metabolomics), and telomere measurements. We map the volume of literature referring to each one of these measurement tools and the extent to which efforts have been made at knowledge integration (e.g., systematic reviews and meta-analyses). We also clarify strengths and weaknesses of the existing platforms and the range of type of samples that can be tested with each of them. These measurement tools can be used in identifying at-risk populations and providing novel markers of survival and treatment response. Rigorous analytic and validation standards, transparent availability of massive data, and integration in large-scale evidence are essential in fulfilling the potential of these technologies.

Health consequences of circadian disruption in humans and animal models

Daily rhythms in behavior and physiology are programmed by a hierarchical collection of biological clocks located throughout the brain and body, known as the circadian system. Mounting evidence indicates that disruption of circadian regulation is associated with a wide variety of adverse health consequences, including increased risk for premature death, cancer, metabolic syndrome, cardiovascular dysfunction, immune dysregulation, reproductive problems, mood disorders, and learning deficits. Here we review the evidence for the pervasive effects of circadian disruption in humans and animal models, drawing from both environmental and genetic studies, and identify questions for future research.

Circadian disruption: potential implications in inflammatory and metabolic diseases associated with alcohol

Circadian rhythms are a prominent and critical feature of cells, tissues, organs, and behavior that help an organism function most efficiently and anticipate things such as food availability. Therefore, it is not surprising that disrupted circadian rhythmicity, a prominent feature of modern-day society, promotes the development and/or progression of a wide variety of diseases, including inflammatory, metabolic, and alcohol-associated disorders. This article will discuss the influence of interplay between alcohol consumption and circadian rhythmicity and how circadian rhythm disruption affects immune function and metabolism as well as potential epigenetic mechanisms that may be contributing to this phenomenon.

Shift work and cancer risk: potential mechanistic roles of circadian disruption, light at night, and sleep deprivation

Shift work that includes a nighttime rotation has become an unavoidable attribute of today's 24-h society. The related disruption of the human circadian time organization leads in the short-term to an array of jet-lag-like symptoms, and in the long-run it may contribute to weight gain/obesity, metabolic syndrome/type II diabetes, and cardiovascular disease. Epidemiologic studies also suggest increased cancer risk, especially for breast cancer, in night and rotating female shift workers. If confirmed in more controlled and detailed studies, the carcinogenic effect of night and shift work will constitute additional serious medical, economic, and social problems for a substantial proportion of the working population. Here, we examine the possible multiple and interconnected cancer-promoting mechanisms as a consequence of shift work, i.e., repeated disruption of the circadian system, pineal hormone melatonin suppression by exposure to light at night, sleep-deprivation-caused impairment of the immune system, plus metabolic changes favoring obesity and generation of proinflammatory reactive oxygen species.

CLOCK, PER2 and BMAL1 DNA methylation: association with obesity and metabolic syndrome characteristics and monounsaturated fat intake

The circadian clock system instructs 24-h rhythmicity on gene expression in essentially all cells, including adipocytes, and epigenetic mechanisms may participate in this regulation. The aim of this research was to investigate the influence of obesity and metabolic syndrome (MetS) features in clock gene methylation and the involvement of these epigenetic modifications in the outcomes. Sixty normal-weight, overweight and obese women followed a 16-weeks weight reduction program. DNA methylation levels at different CpG sites of CLOCK, BMAL1 and PER2 genes were analyzed by Sequenom's MassARRAY in white blood cells obtained before the treatment. Statistical differences between normal-weight and overweight + obese subjects were found in the methylation status of different CpG sites of CLOCK (CpGs 1, 5-6, 8 and 11-14) and, with lower statistical significance, in BMAL1 (CpGs 6-7, 8, 15 and 16-17). The methylation pattern of different CpG sites of the three genes showed significant associations with anthropometric parameters such as body mass index and adiposity, and with a MetS score. Moreover, the baseline methylation levels of CLOCK CpG 1 and PER2 CpGs 2-3 and 25 correlated with the magnitude of weight loss. Interestingly, the percentage of methylation of CLOCK CpGs 1 and 8 showed associations with the intake of monounsaturated and polyunsaturated fatty acids. This study demonstrates for the first time an association between methylation status of CpG sites located in clock genes (CLOCK, BMAL1 and PER2) with obesity, MetS and weight loss. Moreover, the methylation status of different CpG sites in CLOCK and PER2 could be used as biomarkers of weight-loss success, particularly CLOCK CPGs 5-6.

Melatonin production and light exposure of rotating night workers

Decreased melatonin production, due to acute suppression of pineal melatonin secretion by light exposure during night work, has been suggested to underlie higher cancer risks associated with prolonged experience of night work. However, the association between light exposure and melatonin production has never been measured in the field. In this study, 24-h melatonin production and ambulatory light exposure were assessed during both night-shift and day/evening-shift periods in 13 full-time rotating shiftworkers. Melatonin production was estimated with the excretion of urinary 6-sulfatoxymelatonin (aMT6s), and light exposure was measured with an ambulatory photometer. There was no difference in total 24-h aMT6s excretion between the two work periods. The night-shift period was characterized by a desynchrony between melatonin and sleep-wake rhythms, as shown by higher melatonin production during work and lower melatonin production during sleep when working night shifts than when working day/evening shifts. Light exposure during night work showed no correlation with aMT6s excreted during the night of work (p > .5), or with the difference in 24-h aMT6s excretion between the two work periods (p > .1). However, light exposure during night work was negatively correlated with total 24-h aMT6s excretion over the entire night-shift period (p < .01). In conclusion, there was no evidence of direct melatonin suppression during night work in this population. However, higher levels of light exposure during night work may have decreased total melatonin production, possibly by initiating re-entrainment and causing internal desynchrony. This interpretation is consistent with the proposition that circadian disruption, of which decreased melatonin production is only one of the adverse consequences, could be the mediator between night shiftwork and cancer risks.

Epigenetics and lifestyle

The concept of 'lifestyle' includes different factors such as nutrition, behavior, stress, physical activity, working habits, smoking and alcohol consumption. Increasing evidence shows that environmental and lifestyle factors may influence epigenetic mechanisms, such as DNA methylation, histone acetylation and miRNA expression. It has been identified that several lifestyle factors such as diet, obesity, physical activity, tobacco smoking, alcohol consumption, environmental pollutants, psychological stress and working on night shifts might modify epigenetic patterns. Most of the studies conducted so far have been centered on DNA methylation, whereas only a few investigations have studied lifestyle factors in relation to histone modifications and miRNAs. This article reviews current evidence indicating that lifestyle factors might affect human health via epigenetic mechanisms.

Epigenetic impact of long-term shiftwork: pilot evidence from circadian genes and whole-genome methylation analysis

Epigenetic association studies have demonstrated differential promoter methylation in the core circadian genes in breast cancer cases relative to cancer-free controls. The current pilot study aims to investigate whether epigenetic changes affecting breast cancer risk could be caused by circadian disruption through exposure to light at night. Archived DNA samples extracted from whole blood of 117 female subjects from a prospective cohort conducted in Denmark were included in this study. A polymerase chain reaction (PCR)-based method was used for detection of gene-promoter methylation, whereas genome-wide methylation analysis was performed using the Illumina Infinium Methylation Chip. Long-term shiftwork resulted in the same promoter hypomethylation of CLOCK and hypermethylation of CRY2, as was previously observed in breast cancer case-control studies. Genome-wide methylation analysis further discovered widespread methylation alterations in shiftworkers, including changes in many methylation- and cancer-relevant genes. Pathway analysis of the genes with altered methylation patterns revealed several cancer-related pathways. One of the top three networks generated was designated as "DNA replication, recombination, and repair, gene expression, behavior" with ESR1 (estrogen receptor α) featured most prominently in the network, underscoring the potential breast cancer relevance of the genes differentially methylated in long-term shiftworkers. These results, although exploratory, demonstrate the first evidence of the cancer-relevant epigenetic effects of night shiftwork, which warrant further investigation. Considering there are millions of shiftworkers worldwide, understanding the effects of this exposure may lead to novel strategies for cancer prevention and new policies regulating shiftwork.

DNA methylation in repetitive elements and post-traumatic stress disorder: a case-control study of US military service members

AIM

We investigated serum DNA methylation patterns in genomic repetitive elements, LINE-1 and Alu, for post-traumatic stress disorder (PTSD) cases and controls who were US military service members recently deployed to Afghanistan or Iraq.

METHODS

Cases (n = 75) had a postdeployment diagnosis of PTSD. Controls (n = 75) were randomly selected service members with no postdeployment PTSD diagnosis. Pre- and post-deployment sera were accessed, DNA was extracted and DNA methylation (percentage 5-methyl cytosine) was quantified via pyrosequencing. Conditional and unconditional logistic regressions were used to compare: cases post- to pre-deployment; controls post- to pre-deployment; cases to controls predeployment; cases to controls postdeployment.

RESULTS

LINE-1 was hypermethylated in controls post- versus pre-deployment (odds ratio [OR]: 1.33; 95% CI: 1.06-1.65) and hypomethylated in cases versus controls postdeployment (OR: 0.82; 95% CI: 0.67-1.01). Alu was hypermethylated for cases versus controls predeployment (OR: 1.46; 95% CI: 1.08-1.97).

CONCLUSION

Patterns of hypermethylation of LINE-1 in controls postdeployment and of Alu in cases postdeployment are intriguing and may suggest resilience or vulnerability factors.

Interferon-gamma - Inducible Inflammation: Contribution to Aging and Aging-Associated Psychiatric Disorders

Aging is associated with the chronic, low grade, Th-1 type inflammation. The key Th-1 type, pro-inflammatory cytokine, interferon-gamma (IFNG), transcriptionally induces the rate-limiting enzyme of tryptophan (TRY) - kynurenine (KYN) pathway, indoleamine 2,3- dioxygenase (IDO). Activation of IDO shunts TRY metabolism from production of serotonin (substrate of antidepressant effect) and its derivatives: N-acetylserotonin (an agonist to the receptors of brain derived neurotropic factor), and melatonin (regulator of sleep and other circadian rhythms), towards production of KYN and its derivatives (anxiogenic, neurotoxic and pro-oxidant factors). Some of kynurenines up-regulate nitric oxide synthase (NOS). Concurrently with activation of IDO, IFNG induces guanosine triphosphate cyclohydrolase I (GTPCH), the rate limiting enzyme of GTP conversion into BH2 (and increases formation of a stable derivative of BH2, neopterin, at the expense of production of BH4, the mandatory co-factor of NOS). Combination of increased NOS activity (by kynurenines) with decreased formation of BH4 leads to the uncoupling of NOS with consequent shift of arginine metabolism from biosynthesis of NO to formation of superoxide anion and other free radicals, and exacerbation of depression, anxiety and cognitive impairment caused by kynurenines. Polymorphism of IFNG (+874) T/A gene, that encodes production of IFNG protein, impacts the IDO and GTPCH activity that might be assessed in humans by KYN/TRY ratio and neopterin concentrations in biological fluids (e.g., blood, urine and spinal fluid). The hypothesis of IFNG inducible IDO/GTPCH inflammation cascade helps to understand the increased association between aging, inflammation and aging-associated psychiatric and medical (insulin resistance, obesity) disorders. Evaluation of markers of IFNG-inducible inflammation cascade might be used to assess the severity of corresponding behavioral and cognitive changes and the efficacy of pharmacological interventions (e.g., IDO inhibitors).