Does advanced paternal age affect global DNA methylation of human spermatozoa and intracytoplasmic sperm injection outcome?

Objective

This study was performed to (I) evaluate the potential effect of advanced paternal age on global DNA methylation in spermatozoa, and (II) to investigate the association between the outcome of intracytoplasmic sperm injection (ICSI), semen parameters, and advanced paternal age.

Material and Methods

This study comprised 230 semen samples collected from males with a mean age of 38.2±8.5 years. Medical records were used to gather clinical information related to the female partner. The participants were divided into three groups depending on age: age <30 years; age 30-40 years; and age >40 years. The DNA was extracted from purified spermatozoa. Then the sperm global DNA methylation, sperm DNA fragmentation, and chromatin decondensation were evaluated by an ELISA, TUNEL, and Chromomycin A3 staining, respectively.

Results

The sample counts were n=50 (21.8%), n=90 (39.1%) and n=90 (39.1%) for the <30, 30-40 and >40 year age-groups, respectively. A significant variation was found in the age of males included in this study (p<0.001). There was a significant reduction in sperm count, total motility, and non-progressive motility in the older group compared to the younger group (p<0.001). There was also a significant elevation in chromatin decondensation, DNA fragmentation, and global DNA methylation of spermatozoa in the older age group (p<0.001). Finally, there was a significant positive correlation between the percentage of non-motile sperm, sperm chromatin decondensation, DNA fragmentation, global DNA methylation status, and paternal age (p<0.001).

Conclusion

These results suggest that advanced paternal age increased the DNA fragmentation, chromatin decondensation, and global DNA methylation level in human spermatozoa, which negatively affects the ICSI outcomes in couples undergoing ICSI cycles.

Interrelationships and determinants of aging biomarkers in cord blood

BACKGROUND

Increasing evidence supports the concept of prenatal programming as an early factor in the aging process. DNA methylation age (DNAm age), global genome-wide DNA methylation (global methylation), telomere length (TL), and mitochondrial DNA content (mtDNA content) have independently been shown to be markers of aging, but their interrelationship and determinants at birth remain uncertain.

METHODS

We assessed the inter-correlation between the aging biomarkers DNAm age, global methylation, TL and mtDNA content using Pearson's correlation in 190 cord blood samples of the ENVIRONAGE birth cohort. TL and mtDNA content was measured via qPCR, while the DNA methylome was determined using the human 450K methylation Illumina microarray. Subsequently, DNAm age was calculated according to Horvath's epigenetic clock, and mean global, promoter, gene-body, and intergenic DNA methylation were determined. Path analysis, a form of structural equation modeling, was performed to disentangle the complex causal relationships among the aging biomarkers and their potential determinants.

RESULTS

DNAm age was inversely correlated with global methylation (r = -0.64, p < 0.001) and mtDNA content (r = - 0.16, p = 0.027). Cord blood TL was correlated with mtDNA content (r = 0.26, p < 0.001) but not with global methylation or DNAm age. Path analysis showed the strongest effect for global methylation on DNAm age with a decrease of 0.64 standard deviations (SD) in DNAm age for each SD (0.01%) increase in global methylation (p < 0.001). Among the applied covariates, newborn sex and season of delivery were the strongest determinants of aging biomarkers.

CONCLUSIONS

We provide insight into molecular aging signatures at the start of life, including their interrelations and determinants, showing that cord blood DNAm age is inversely associated with global methylation and mtDNA content but not with newborn telomere length. Our findings demonstrate that cord blood TL and DNAm age relate to different pathways/mechanisms of biological aging and can be influenced by environmental factors already at the start of life. These findings are relevant for understanding fetal programming and for the early prevention of noncommunicable diseases.

Cigarette heavy smoking alters DNA methylation patterns and gene transcription levels in humans spermatozoa

Tobacco smoking is considered the most common reason of death and infertility around the world. This study was designed to assess the impact of tobacco heavy smoking on sperm DNA methylation patterns and to determine whether the transcription level of ALDH3B2, PTGIR, PRICKLE2, and ALS2CR12 genes is different in heavy smokers compared to non-smokers. As a screening study, the 450 K array was used to assess the alteration in DNA methylation patterns between heavy smokers (n = 15) and non-smokers (n = 15). Then, four CpGs that have the highest difference in methylation level (cg16338278, cg08408433, cg05799088, and cg07227024) were selected for validation using deep bisulfite sequencing in an independent cohort of heavy smokers (n = 200) and non-smokers (n = 100). A significant variation was found between heavy smokers and non-smokers in the methylation level at all CpGs within the PRICKLE2 and ALS2CR12 gene amplicon (P < 0.001). Similarly, a significant variation was found in the methylation level at nine out of thirteen CpGs within the ALDH3B2 gene amplicon (P < 0.01). Additionally, eighteen CpGs out of the twenty-six within the PTGIR gene amplicon have a significant difference in the methylation level between heavy smokers and non-smokers (P < 0.01). The study showed a significant difference in sperm global DNA methylation, chromatin non-condensation, and DNA fragmentation (P < 0.001) between heavy smokers and non-smokers. A significant decline was shown in the transcription level of ALDH3B2, PTGIR, PRICKLE2, and ALS2CR12 genes (P < 0.001) in heavy smokers. In conclusion, heavy smoking influences DNA methylation at several CpGs, sperm global DNA methylation, and transcription level of the PRICKLE2, ALS2CR12, ALDH3B2, and PTGIR genes, which affects negatively the semen parameters of heavy smokers.

Multiplexed magnetic beads-assisted amperometric bioplatforms for global detection of methylations in nucleic acids

This work reports the first electrochemical bioplatform developed for the multidetection of 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) in DNA, DNA N6-methyladenine (6mA) and RNA N6-methyladenosine (m6A) methylations at global level. Direct competitive immunoassays were implemented on the surface of magnetic beads (MBs) and optimized for the single amperometric determination of different targets varying in length, sequence and number of methylations on screen-printed carbon electrodes. After evaluating the sensitivity and selectivity of such determinations and the confirmation of no cross-reactivity, a multiplexed disposable platform allowing the simultaneous determination of the mentioned four methylation events in only 45 min has been prepared. The multiplexed bioplatform was successfully applied to the determination of m6A in cellular total RNA and of 5-mC, 5-hmC and 6mA in genomic DNA extracted from tissues. The developed bioplatform showed its usefulness to discriminate the aggressiveness of cancerous cells and between healthy and tumor tissues of colorectal cancer patients.

Evaluation of the influence of global DNA methylation level in patients with acute coronary syndrome

DNA methylation is one of the mechanisms of epigenetic regulation and is observed in mammals to maintain a normal expression pattern of the genes. Aberrant profiles of DNA methylation have already been associated with cardiovascular diseases. We evaluated 190 patients with Acute Coronary Syndrome (ACS) and 75 patients without ACS (non-ACS). Patient severity was assessed by the TIMI risk score, and both levels of global DNA methylation (ACS = 190; non-ACS = 75), stratified in expected group (male ≥ 65 years; female ≥ 55 years) and early group (male < 65 years; female < 55 years). As results, the ACS and non-ACS groups showed different levels of global DNA methylation, and patients with ACS were more methylated (p = 0.0121). Patients with ACS, showed a difference (p < 0.0001) in methylation profiles between groups. The low TIMI group had a higher level of DNA methylation, while the intermediate / high group showed a decreased methylation pattern. A negative correlation was observed between the level of global methylation and the increase in age (p = 0.0387; r = -0.15), which became hypomethylated over the years. The hypermethylated global DNA profile by its association with the development of ACS can be a potential biomarker.

Differential global and MTHFR gene specific methylation patterns in preeclampsia and recurrent miscarriages: A case-control study from North India

AIM

The purpose of the present study is to evaluate and understand the association of global and MTHFR gene specific methylation in preeclampsia and recurrent miscarriages in light of MTHFR C677T polymorphism.

METHODS

The subjects comprised of recurrent miscarriage cases, their gestation matched controls, preeclampsia cases and matched controls. A set of women at full term were also recruited. Fasting blood sample (~5 ml) was drawn from all the participants followed by DNA extraction, global DNA methylation and MTHFR gene specific methylation. MTHFR C677T polymorphism was analysed by PCR followed by RFLP.

RESULTS HIGHER

Global DNA methylation at maternal front (p = 0.04) and hypomethylation of MTHFR gene at fetal front (p = 0.001) might be a characteristic of preeclampsia. Recurrent miscarriage cases were having significantly (p = 0.002) hyper MTHFR gene specific methylation as compared to controls. Women carrying CT genotype were found to be having significantly (p = 0.001) higher global DNA methylation in PE cases and MTHFR gene specific methylation (p = 0.005) in RM cases. Intergenerational analysis revealed similar patterns of global DNA methylation and MTHFR gene specific methylation among both PE and RM cases at maternal and fetal fronts.

CONCLUSION

The study highlights the importance of global DNA methylation in Preeclampsia and MTHFR gene specific methylation in recurrent miscarriages. MTHFR C677T gene polymorphism in association with global and gene specific methylation seem to play a pivotal role in PE and RM respectively.

Idiopathic male infertility is strongly associated with aberrant DNA methylation of imprinted loci in sperm: a case-control study

BACKGROUND

Male infertility is a complex disease caused by a combination of genetic, environmental, and lifestyle factors. Abnormal epigenetic programming has been proposed as a possible mechanism compromising male fertility. Recent studies suggest that aberrant imprinting in spermatozoa in a subset of infertile men is a risk factor for congenital diseases in children conceived via assisted reproduction techniques. In this study, we examined the DNA methylation status of CpG sites within the differentially methylated regions (DMRs) of three imprinted genes, H19, GNAS, and DIRAS3, using combined bisulfite PCR restriction analysis and bisulfite sequencing in sperm obtained from 135 men with idiopathic male infertility, including normozoospermia (n = 39), moderate oligozoospermia (n = 45), and severe oligozoospermia (n = 51), and fertile controls (n = 59). The percentage of global methylation was compared between fertile controls and infertile patients displaying abnormal DNA methylation status of imprinted loci. Moreover, we also analyzed whether the DNA methyltransferases (DNMTs) polymorphisms impact upon the methylation patterns of imprinted genes in idiopathic infertile males.

RESULTS

Aberrant methylation patterns of imprinted genes were more prevalent in idiopathic infertile males, especially in patients with oligozoospermia. Infertile males with aberrant methylation patterns of imprinted genes displayed a tendency of lower global methylation levels, although not reaching statistical significance (P = 0.13). In the genotype-epigenotype correlation analysis, no significant association was observed between aberrant methylation patterns of the three imprinted genes and genotypes of the four DNA methyltransferase (DNMT) genes.

CONCLUSION

We conclude that abnormalities of DMR within imprinted genes may be associated with idiopathic male infertility. Disruption in methylation pattern of the three imprinted genes does not occur in high-risk genotypes of DNMTs.

Prenatal exposure to persistent organic pollutants and methylation of LINE-1 and imprinted genes in placenta: A CHECK cohort study

Prenatal exposure to persistent organic pollutants (POPs) has been linked to numerous adverse birth outcomes among newborn infants in many epidemiological studies. Although epigenetic modifications have been suggested as possible explanations for those associations, studies have rarely reported a relationship between POP exposure during pregnancy and DNA methylation in the placenta. In the present study, we investigated the association between prenatal exposure to several POPs, including organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs), and methylation levels of long interspersed element 1 (LINE-1), as well as imprinted genes in placental DNAs among Korean mother-child pairs (N = 109). We assessed the association of DNA methylation not only with each target POP (single-POP models) but also with multiple POPs applying principal component analysis (multiple-POP models). Potential associations between placental DNA methylation and birth outcomes of newborn infants were also estimated. In single-POP models, significant associations were detected between OCP measurements and placental DNA methylation. Elevated concentrations of β-hexachlorhexane (β-HCH) in maternal serum collected during delivery were significantly associated with a decrease in methylation of LINE-1 in the placenta. Higher levels of p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) in maternal serum were associated with hypermethylation of insulin-like growth factor 2 (IGF2). In multiple-POP models, a significant and positive association between DDTs and IGF2 methylation was also observed. Placental LINE-1 methylation was inversely associated with birth length. Our observations indicate that prenatal exposure to several POPs including DDTs is associated with the changes in methylation of genes, including major imprinted genes in the placenta. The consequences of these epigenetic alterations in placenta during development deserve further investigation.

LINE-1 is preferentially hypomethylated within adenomatous polyps in the presence of synchronous colorectal cancer

Background

Conventional tubular adenomas are frequently detected in patients undergoing average risk screening colonoscopy and are over-represented in patients who will develop colorectal cancer (CRC). Whether features of adenomas could serve as predictors of synchronous CRC is not known. Here, we investigate whether global methylation markers, including LINE-1, differ within adenomas in patients with and without synchronous CRC.

Methods

Colorectal tubular/tubulovillous adenomatous polyps in the absence (P group, n = 45) and in the presence of synchronous CRC (PC group, n = 32) were identified. Global methylation and demethylation by ELISA for 5-methylcytosine (5-mC) and 5-hydroxymethyl cytosine (5-hmC), respectively, were assessed in polyps and adjacent normal non-neoplastic tissue. LINE-1 hypomethylation was assessed by pyrosequencing of bisulfite-converted DNA as well.

Results

Global methylation (5-mC) showed no differences in overall methylation status in the adenomatous polyps in the two groups (5-mC relative to control %, PC group 0.117; P group 0.161, p = 0.148). Global hydroxymethylation 5-hmC was also not significantly different in adenomatous polyps of the PC group than in those of the P group (0.0059 vs 0.0097, p = 0.681). Similarly, global 5-hmC was not different between normal tissues from patients without neoplasia in comparison to those from CRC patients (0.0461 ± 0.080 vs 0.039 ± 0.159, p = 0.215). In contrast, adenomatous polyps of the PC group had lower levels of LINE-1 methylation compared to the adenomas in the P group (53.07 ± 4.5 vs 59.95 ± 5.4, p < 0.001). LINE-1 methylation was also significantly lower in the normal tissue from cancer patients compared to that from patients without any neoplasia (58.07 ± 3.78 vs 71.50 ± 6.47, p < 0.001).

Conclusions

LINE-1 hypomethylation of precancerous adenomas correlates with the presence of synchronous CRC. Measurement of DNA hypomethylation levels of colorectal adenomas by LINE-1 could have future implications in approaches to defining CRC risk in screening programs.

Electrochemical biosensing strategies for DNA methylation analysis

DNA methylation is one of the key epigenetic modifications of DNA that results from the enzymatic addition of a methyl group at the fifth carbon of the cytosine base. It plays a crucial role in cellular development, genomic stability and gene expression. Aberrant DNA methylation is responsible for the pathogenesis of many diseases including cancers. Over the past several decades, many methodologies have been developed to detect DNA methylation. These methodologies range from classical molecular biology and optical approaches, such as bisulfite sequencing, microarrays, quantitative real-time PCR, colorimetry, Raman spectroscopy to the more recent electrochemical approaches. Among these, electrochemical approaches offer sensitive, simple, specific, rapid, and cost-effective analysis of DNA methylation. Additionally, electrochemical methods are highly amenable to miniaturization and possess the potential to be multiplexed. In recent years, several reviews have provided information on the detection strategies of DNA methylation. However, to date, there is no comprehensive evaluation of electrochemical DNA methylation detection strategies. Herein, we address the recent developments of electrochemical DNA methylation detection approaches. Furthermore, we highlight the major technical and biological challenges involved in these strategies and provide suggestions for the future direction of this important field.

Prenatal airborne polycyclic aromatic hydrocarbon exposure, LINE1 methylation and child development in a Chinese cohort

BACKGROUND

Polycyclic aromatic hydrocarbons (PAH) are carcinogenic, neurotoxic environmental pollutants generated during incomplete combustion of fossil fuel and other organic material. PAH exposure has been associated with adverse fetal development and epigenetic alterations in cord blood. Several molecular epidemiology studies have established PAH-DNA adducts as biomarkers of PAH exposure.

OBJECTIVES

We investigated the relationship between LINE1 DNA methylation and PAH-DNA adduct levels in cord blood, and with neurodevelopmental outcomes.

METHODS

In Tongliang County, China, the current study enrolled two population-based cohorts of nonsmoking pregnant women before (2002) and after (2005) the closure of a local coal-fired power plant in May 2004. We analyzed cord blood samples collected from mothers in the two cohorts (n=110 from 2002 cohort and n=107 from 2005 cohort) for PAH-DNA adducts and genomic LINE1 DNA methylation. Neurodevelopmental data on children were collected using the Gesell Developmental Scales (GDS) at age 2 and using the Wechsler Intelligence Scale for Children (WISC) at age 5.

RESULTS

A significant inverse relationship was observed between PAH-DNA adducts and LINE1 DNA methylation (β=-0.010, p<0.038). A significant, positive association between LINE1 methylation and scores on WISC full scale and verbal (β=85.31, p<0.005; β=94.36, p<0.003) but not on the GDS. Mediation analysis did not find LINE1 to be a direct mediator between PAH-DNA adducts and IQ score.

CONCLUSION

LINE1 methylation in cord blood DNA was a positive predictor of IQ at age 5 and was decreased at higher levels of prenatal PAH exposure measured by PAH-DNA adducts in cord blood. However, the adverse effects of prenatal exposure to PAH on IQ scores did not appear to be directly mediated by altered LINE1 methylation.

Analysis of DNA Methylation by Pyrosequencing

Pyrosequencing is a technique that uses a sequencing-by-synthesis system which is designed to quantify single-nucleotide polymorphisms (SNPs). Artificial C/T SNP creation via bisulfite modification permits measurement of DNA methylation locally and globally in real time. Alteration in DNA methylation has been implicated in aging, as well as aging-related conditions such as cancer, as well as cardiovascular, neurodegenerative, and autoimmune diseases. Considering its ubiquitous presence in divergent clinical pathologies, quantitative analysis of DNA CpG methylation both globally and at individual genes helps to elucidate the regulation of genes involved in pathophysiological conditions. The ability to detect and quantify the methylation pattern of DNA has the potential to serve as an early detection marker and potential drug target for several diseases. Here, we provide a detailed technical protocol for pyrosequencing supplemented by critical information about assay design and nuances of the system that provides a strong foundation for beginners in the field.

Epigenetic modulation of Chlorella (Chlorella vulgaris) on exposure to polycyclic aromatic hydrocarbons

DNA methylation in promoter region can be a new chemopreventive marker against polycyclic aromatic hydrocarbons (PAHs). We performed a randomized, double blind and cross-over trial (N=12 healthy females) to evaluate chlorella (Chlorella vulgaris)-induced epigenetic modulation on exposure to PAHs. The subjects consumed 4 tablets of placebo or chlorella supplement (total chlorophyll ≈ 8.3mg/tablet) three times a day before meals for 2 weeks. When the subjects consumed chlorella, status of global hypermethylation (5-methylcytosine) was reduced, compared to placebo (p=0.04). However, DNA methylation at the DNMT1 or NQO1 was not modified by chlorella. We observed the reduced levels of urinary 1-hydroxypyrene (1-OHP), a typical metabolite of PAHs, by chlorella intake (p<0.1) and a positive association between chlorella-induced changes in global hypermethylation and urinary 1-OHP (p<0.01). Therefore, our study suggests chlorella works for PAH-detoxification through the epigenetic modulation, the interference of ADME of PAHs and the interaction of mechanisms.

Inter-locus as well as intra-locus heterogeneity in LINE-1 promoter methylation in common human cancers suggests selective demethylation pressure at specific CpGs

Background

Hypomethylation of long interspersed element (LINE)-1 has been observed in tumorigenesis when using degenerate assays, which provide an average across all repeats. However, it is unknown whether individual LINE-1 loci or different CpGs within one specific LINE-1 promoter are equally affected by methylation changes. Conceivably, studying methylation changes at specific LINE-1 may be more informative than global assays for cancer diagnostics. Therefore, with the aim of mapping methylation at individual LINE-1 loci at single-CpG resolution and exploring the diagnostic potential of individual LINE-1 locus methylation, we analyzed methylation at 11 loci by pyrosequencing, next-generation bisulfite sequencing as well as global LINE-1 methylation in bladder, colon, pancreas, prostate, and stomach cancers compared to paired normal tissues and in blood samples from some of the patients compared to healthy donors.

Results

Most (72/80) tumor samples harbored significant methylation changes at at least one locus. Notably, our data revealed not only the expected hypomethylation but also hypermethylation at some loci. Specific CpGs within the LINE-1 consensus sequence appeared preferentially hypomethylated suggesting that these could act as seeds for hypomethylation. In silico analysis revealed that these CpG sites more likely faced the histones in the nucleosome. Multivariate logistic regression analysis did not reveal a significant clinical advantage of locus-specific methylation markers over global methylation markers in distinguishing tumors from normal tissues.

Conclusions

Methylation changes at individual LINE-1 loci are heterogeneous, whereas specific CpGs within the consensus sequence appear to be more prone to hypomethylation. With a broader selection of loci, locus-specific LINE-1 methylation could become a tool for tumor detection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-015-0051-y) contains supplementary material, which is available to authorized users.

Indoor air pollution from solid fuels and peripheral blood DNA methylation: findings from a population study in Warsaw, Poland

DNA methylation is a potential mechanism linking indoor air pollution to adverse health effects. Fetal and early-life environmental exposures have been associated with altered DNA methylation and play a critical role in progress of diseases in adulthood. We investigated whether exposure to indoor air pollution from solid fuels at different lifetime periods was associated with global DNA methylation and methylation at the IFG2/H19 imprinting control region (ICR) in a population-based sample of non-smoking women from Warsaw, Poland. Global methylation and IFG2/H19 ICR methylation were assessed in peripheral blood DNA from 42 non-smoking women with Luminometric Methylation Assay (LUMA) and quantitative pyrosequencing, respectively. Linear regression models were applied to estimate associations between indoor air pollution and DNA methylation in the blood. Compared to women without exposure, the levels of LUMA methylation for women who had ever exposed to both coal and wood were reduced 6.70% (95% CI: -13.36, -0.04). Using both coal and wood before age 20 was associated with 6.95% decreased LUMA methylation (95% CI: -13.79, -0.11). Further, the negative correlations were more significant with exposure to solid fuels for cooking before age 20. There were no clear associations between indoor solid fuels exposure before age 20 and through the lifetime and IFG2/H19 ICR methylation. Our study of non-smoking women supports the hypothesis that exposure to indoor air pollution from solid fuels, even early-life exposure, has the capacity to modify DNA methylation that can be detected in peripheral blood.

The association between personal sun exposure, serum vitamin D and global methylation in human lymphocytes in a population of healthy adults in South Australia

BACKGROUND

There is a positive association between solar UV exposure and micronucleus frequency in peripheral blood lymphocytes (PBL) and this association may be stronger when serum vitamin D (25(OH)D) levels are insufficient (<50 nmol/L). Micronucleus formation can result from global hypomethylation of DNA repeat sequences. The aim of this analysis was to evaluate the relationship between solar UV exposure and methylation pattern in LINE-1 repetitive elements in PBL DNA and to see if serum 25(OH)D levels modify it.

METHOD

Personal solar UV exposure was estimated from hours of outdoor exposure over 6 weeks recalled at the time of blood collection in 208 male and female participants living in South Australia. Methylation in LINE-1 repetitive elements was assessed in PBL using pyrosequencing.

RESULTS

Methylation in LINE-1 decreased with increasing solar UV exposure (% decrease = 0.5% per doubling of sUV; 95%CI: -0.7 to -0.2 p(value) = 0.00003). Although there was no correlation between LINE-1 methylation and micronucleus frequency, there was a 4.3% increase (95%CI: 0.6-8.1 p-value = 0.02) in nucleoplasmic bridges and a 4.3% increase in necrosis (CI: 1.9-6.8 p-value = 0.0005) for every 1% increase in LINE-1 methylation. Serum 25(OH)D was not associated with DNA methylation; or did it modify the association of solar UV with DNA methylation.

CONCLUSION

Exposure to solar UV radiation may reduce DNA methylation in circulating lymphocytes. This association does not appear to be influenced or mediated by vitamin D status.

DNA methylation in paired breast epithelial and white blood cells from women undergoing reduction mammoplasty

BACKGROUND

The extent to which white blood cell (WBC) DNA methylation provides information on the status of breast epithelial cell DNA is unknown.

PATIENTS AND METHODS

We examined the correlation between methylation in Ras-association domain family-1 gene (RASSF1), a tumor-suppressor gene, and methylation in repetitive elements in paired sets of DNA from WBC and breast epithelial cells collected from 32 women undergoing reduction mammoplasty.

RESULTS

We observed no evidence of correlation in methylation levels for ALU, long interspersed nuclear element-1 (LINE1) or juxtacentromeric satellite-2 (SAT2) (r=0.02 for LINE1, p=0.98; r=0.28 for ALU, p=0.12; r=0.26 for SAT2, p=0.17) for matched sets of DNA from WBC and breast epithelial cells. Variability in these markers across individuals and in the same tissue was low. Five women had an average methylation level above 5% for RASSF1 in breast epithelial cell DNA; however, average methylation levels in WBC DNA for these women were all below 1%.

CONCLUSION

Methylation patterns in WBC DNA did not reflect methylation patterns in the breast.

Maternal micronutrients and brain global methylation patterns in the offspring

OBJECTIVES

Studies have established the association of maternal nutrition and increased risk for non-communicable diseases. It has been suggested that this involves epigenetic modifications in the genome. However, the role of maternal micronutrients in the one-carbon cycle in influencing brain development of the offspring through methylation is unexplored. It is also unclear whether epigenomic marks established during early development can be reversed by a postnatal diet. The present study reports the effect of maternal micronutrients and omega-3 fatty acids on global DNA methylation patterns in the brain of the Wistar rat offspring at three timepoints (at birth, postnatal day 21, and 3 months of age).

METHOD

Pregnant rats were divided into control (n = 8) and five treatment groups (n = 16 dams in each group) at two levels of folic acid (normal and excess folate) in the presence and absence of vitamin B12 (NFBD, EFB, and EFBD). Omega-3 fatty acid supplementation was given to vitamin B12 deficient groups (NFBDO and EFBDO). Following delivery, eight dams from each group were shifted to control diet and remaining continued on the same treatment diet.

RESULTS

Our results demonstrate that maternal micronutrient imbalance results in global hypomethylation in the offspring brain at birth. At adult age the cortex of the offspring displayed hypermethylation as compared with control, in spite of a postnatal control diet. In contrast, prenatal omega-3 fatty acid supplementation was able to normalize methylation at 3 months of age.

DISCUSSION

Our findings provide clues for the role of omega-3 fatty acids in reversing methylation patterns thereby highlighting its contribution in neuroprotection and cognition.