Distinctive patterns of age-dependent hypomethylation in interspersed repetitive sequences

Types of DNA methylation status of the interspersed repetitive sequences for LINE-1, Alu, HERV-E and HERV-K in the neutrophils from systemic lupus erythematosus patients and healthy controls

Changes of the DNA methylation at the interspersed repetitive sequences can occur in various conditions including cancer as well as autoimmune diseases. We previously reported the hypomethylation of LINE-1 and HERV-E in the lymphocytes of systemic lupus erythematosus (SLE) patients. As neutrophils are another important cell type contributing to SLE pathogenesis, in this study, we evaluated the methylation levels and patterns for LINE-1, ALU, HERV-E and HERV-K in the neutrophils from SLE patients compared with the healthy controls. We observed that the methylation levels, especially for LINE-1, in the neutrophils from SLE patients were significantly lower than the healthy controls (P-value < 0.0001). Interestingly, this hypomethylation was not correlated with the activity of the disease. Furthermore, the methylation levels and patterns for Alu, HERV-E and HERV-K in the neutrophils from the SLE patients were not significantly different from the healthy controls. In addition, we further investigated whether there were any correlations between the intragenic LINE-1 and differential expressions of the neutrophils from the SLE patients using public arrays data. The upregulated genes in the neutrophils from the SLE patients were significantly associated with the genes containing LINE-1s compared with the healthy controls (P-value GSE27427 = 7.74 × 10(-3); odds ratio (OR) = 1.28). Interestingly, this association was mainly found among genes with antisense LINE-1s (P-value GSE27427 = 6.22 × 10(-3); OR = 1.38). Bioinformatics data suggest that LINE-1 hypomethylation may affect expression of the genes that may contribute to the pathogenesis of SLE. However, additional functional studies of these proposed genes are warranted to prove this hypothesis.

Identification and association study with lung cancer for novel insertion polymorphisms of human endogenous retrovirus

Sequences of human endogenous retroviruses (HERVs) are members of the long terminal repeat (LTR) retrotransposon family. Although the expression of HERV has long been a topic of investigation, HERV-insertion polymorphisms are not well known, and a genetic association between HERV-insertion polymorphisms and cancer has never been reported. To identify novel HERV loci in the genome from cancer tissues, we carried out the inverse PCR method targeting a conserved LTR region of HML-2, which is the most recently acquired HERV group. Novel two insertions, HML-2_sLTR(1p13.2) and HML-2_sLTR(19q12), were identified as insertionally polymorphic solo LTRs. Furthermore, a significant prevalence of HML-2_sLTR(1p13.2) homozygosity was detected in female never-smoking patients aged 60 years and over who had lung adenocarcinoma [versus the other genotyping; odds ratio (OR): 1.97; 95% confidence interval (CI): 1.01-3.81]. In another cohort consisting of female never-smoking patients with lung adenocarcinoma, a prevalence of HML-2_sLTR(1p13.2) homozygosity tended to be high in patients aged 60 years and over (versus the other genotyping; OR: 2.03; 95% CI: 0.96-4.29), whereas a low prevalence of HML-2_sLTR(1p13.2) homozygosity was detected in patients <60 years old (versus the other genotyping; OR: 0.31; 95% CI: 0.11-0.94). Our results suggest that HML-2_sLTR(1p13.2) is involved with the susceptibility to lung adenocarcinoma in female never-smokers in an age-dependent manner and that other HERV polymorphisms related to human diseases might remain to be identified in the human genome.

Epigenetic consequences of a changing human diet

The human diet has undergone profound changes over recent generations and this trend is likely to accelerate in the 21st century. Innovations in food technology, new ways of producing and processing foods and the increasing use of artificial vitamins and novel ingredients are changing the human diet in ways that our dietary monitoring systems struggle to keep pace with. There is a growing awareness of the importance of diet, but little understanding of how these changes may affect the health of current and future generations. Epigenetic programming, and specifically the persistence of functional epigenetic states following nutritional exposure, is particularly relevant to the issue of dietary change. Epigenetics is emerging as perhaps the most important mechanism through which diet and nutrition can directly influence the genome and there is now considerable evidence for nutritional epigenetic programming of health and the response to diet itself. A number of nutrients and food components that are changing in the human diet have been shown to produce epigenetic states that are stable across different timescales. We need to better understand the nutritional programming of epigenetic states, the persistence of these marks in time and their effect on biological function and the response to diet.

Hypomethylation of Alu elements in post-menopausal women with osteoporosis

A decrease in genomic methylation commonly occurs in aging cells; however, whether this epigenetic modification leads to age-related phenotypes has not been evaluated. Alu elements are the major interspersed repetitive DNA elements in humans that lose DNA methylation in aging individuals. Alu demethylation in blood cells starts at approximately 40 years of age, and the degree of Alu hypomethylation increases with age. Bone mass is lost with aging, particularly in menopausal women with lower body mass. Consequently, osteoporosis is commonly found in thin postmenopausal women. Here, we correlated the Alu methylation level of blood cells with bone density in 323 postmenopausal women. Alu hypomethylation was associated with advanced age and lower bone mass density, (P<0.05). The association between the Alu methylation level and bone mass was independent of age, body mass, and body fat, with an odds ratio [1]  = 0.4316 (0.2087-0.8927). Individuals of the same age with osteopenia, osteoporosis, and a high body mass index have lower Alu methylation levels (P = 0.0005, 0.003, and ≤0.0001, respectively). Finally, when comparing individuals with the same age and body mass, Alu hypomethylation was observed in individuals with lower bone mass (P<0.0001). In conclusion, there are positive correlations between Alu hypomethylation in blood cells and several age-related phenotypes in bone and body fat. Therefore, reduced global methylation may play a role in the systemic senescence process. Further evaluation of Alu hypomethylation may clarify the epigenetic regulation of osteoporosis in post-menopausal women.

LINE-1 methylation in peripheral blood and the risk of melanoma in melanoma-prone families with and without CDKN2A mutations

Cutaneous malignant melanoma (CMM) is an etiologically heterogenous disease with genetic, environmental (sun exposure), and host (pigmentation/nevi) factors and their interactions contributing to risk. Recently, epigenetic changes involving reduced levels of global DNA methylation in blood have been associated with genomic instability and cancer risk. We thus examined whether global methylation was associated with CMM risk in individuals from melanoma-prone families with and without CDKN2A germline mutations. We measured global DNA methylation using bisulfite pyrosequencing at four CpG sites of the long interspersed nucleotide element-1 (LINE-1) sequences in peripheral blood mononuclear cells (PBMCs) from individuals in 64 melanoma-prone families including 114 CMM cases (45 CDKN2A-positive and 69 CDKN2A-negative) and 121 unaffected individuals (31 CDKN2A-positive and 90 CDKN2A-negative). We used unconditional logistic regression to evaluate the association between CMM status and LINE-1 methylation levels, adjusting for age at blood draw and accounting for familial correlation in the variance. We found that male sex was significantly associated with higher overall LINE-1 methylation (P=0.0001). However, the overall and site-specific levels of LINE-1 methylation did not vary significantly by CMM status (overall odds ratio: 1.57, 95% confidence interval: 0.84-2.95, P=0.16; comparing lowest to highest or reference methylation group). Similar results were obtained when CDKN2A-positive and CDKN2A-negative families were analyzed separately. Our findings did not support a significant association between constitutional LINE-1 methylation in PBMCs and risk of CMM in melanoma-prone families with or without CDKN2A mutations.

Expression of a LINE-1 endonuclease variant in gastric cancer: its association with clinicopathological parameters

Background

Long interspersed nuclear element-1 (LINE-1 or L1), the most abundant and only autonomously active family of non-LTR retrotransposons in the human genome, expressed not only in the germ lines but also in somatic tissues. It contributes to genetic instability, aging, and age-related diseases, such as cancer. Our previous study identified in human gastric adenocarcinoma an upregulated transcript GCRG213, which shared 88% homology with human L1 sequence and contained a putative conserved apurinic/apyrimidinic endonucleas1 domain.

Methods

Immunohistochemistry was carried out by using a monoclonal mouse anti-human GCRG213 protein (GCRG213p) antibody produced in our laboratory, on tissue microarray constructed with specimens from 175 gastric adenocarcinoma patients. The correlation between GCRG213p expression and patient clinicopathological parameters was evaluated. GCRG213p expression in gastric cancer cell lines were studied using Western blotting analysis. L1 promoter methylation status of gastric cancer cells was tested using methylation-specific PCR. BLASTP was used at the NCBI Blast server to identify GCRG213p sequence to any alignments in the Protein Data Bank databases.

Results

Most primary gastric cancer, lymph node metastases and gastric intestinal metaplasia glands showed positive GCRG213p immunoreactivity. High GCRG213p immunostaining score in the primary gastric cancer was positively correlated with tumor differentiation (well differentiated, p = 0.001), Lauren’s classification (intestinal type, p < 0.05) and a late age onset of gastric adenocarcinoma (≥65 yrs; p < 0.05). GCRG213p expression has no association with other clinicopathological parameters, including survival. Western blotting analysis of GCRG213p expression in gastric cancer cells indicated that GCRG213p level was higher in gastric cancer cell lines than in human normal gastric epithelium immortalized cell line GES-1. Partial methylation of L1 in gastric cancer cells was confirmed by methylation-specific PCR. BLASTP program analysis revealed that GCRG213p peptide shared 83.0% alignment with the C-terminal region of L1 endonuclease (L1-EN). GCRG213p sequence possesses the important residues that compose the conserved features of L1-EN.

Conclusions

GCRG213p could be a variant of L1-EN, a functional member of L1-EN family. Overexpression of GCRG213p is common in both primary gastric cancer and lymph node metastasis. These findings provide evidence of somatic L1 expression in gastric cancer, and its potential consequences in the form of tumor.

Do age-related changes in DNA methylation play a role in the development of age-related diseases?

DNA methylation is an important epigenetic mechanism in mammalian cells. It occurs almost exclusively at CpG sites and has a key role in a number of biological processes. It plays an important part in regulating chromatin structure and has been best studied for its role in controlling gene expression. In particular, hypermethylation of gene promoters which have high levels of CpG sites, known as CpG islands, leads to gene inactivation. In healthy cells, however, it appears that only a small number of genes are controlled through promoter hypermethylation, such as genes on the inactivated X-chromosome or at imprinted loci, and most promoter-associated CpG islands remain methylation-free regardless of gene expression status. However, a large body of evidence has now shown that this protection from methylation not only breaks down in a number of pathological conditions (e.g. cancer), but also already occurs during the normal process of aging. The present review focuses on the methylation changes that occur during healthy aging and during disease development, and the potential links between them. We focus especially on the extent to which the acquisition of aberrant methylation changes during aging could underlie the development of a number of important age-related pathological conditions.

DNA methylation of human endogenous retrovirus in systemic lupus erythematosus

Previous studies have reported that T cells from active systemic lupus erythematosus (SLE) patients contained global hypomethylation and demethylation at the promoter of several genes, which may contribute to the pathogenesis of the disease. Currently there are scarce data on methylation of retroelements in patients with SLE. We estimated and compared the methylated levels of human endogenous retroviruses (HERV)-E and HERV-K in normal and SLE CD3+CD4+ T lymphocytes, CD8+ T and B lymphocytes by using combined bisulfite restriction analysis-interspersed repetitive sequences (COBRA-IRS). HERV-E LTR2C methylation level in CD3+CD4+ T lymphocytes of active SLE was significantly lower than inactive SLE and normal controls (P=0.023 and 0.035, respectively). Surprisingly, HERV-K LTR5_Hs hypomethylation was significantly detected in CD3+CD4+ T lymphocytes from patients with inactive SLE when compared with the active SLE and normal controls (P=0.027 and 0.002, respectively). Demethylation of HERV-K LTR5_Hs in B cells was also detected when compared with the normal controls (P=0.048). Furthermore, the hypomethylation of HERV-E LTR2C in CD3+CD4+ T lymphocytes was positively correlated with lymphopenia in active SLE, whereas the hypomethylation of HERV-K LTR5_Hs was significantly correlated with complement activity and Systemic Lupus Erythematosus Disease Activity Index score. In summary, for each lymphocyte subset in patients with SLE, IRS hypomethylation was found to be type specific. Further studies are needed to confirm and explain these observations.

A lower degree of PBMC L1 methylation is associated with excess body weight and higher HOMA-IR in the presence of lower concentrations of plasma folate

BACKGROUND

Identification of associations between global DNA methylation and excess body weight (EBW) and related diseases and their modifying factors are an unmet research need that may lead to decreasing DNA methylation-associated disease risks in humans. The purpose of the current study was to evaluate the following; 1) Association between the degree of peripheral blood mononuclear cell (PBMC) L1 methylation and folate, and indicators of EBW, 2) Association between the degree of PBMC L1 methylation and folate, and insulin resistance (IR) as indicated by a higher homeostasis model assessment (HOMA-IR).

METHODS

The study population consisted of 470 child-bearing age women diagnosed with abnormal pap. The degree of PBMC L1 methylation was assessed by pyrosequencing. Logistic regression models specified indicators of EBW (body mass index-BMI, body fat-BF and waist circumference-WC) or HOMA-IR as dependent variables and the degree of PBMC L1 methylation and circulating concentrations of folate as the independent predictor of primary interest.

RESULTS

Women with a lower degree of PBMC L1 methylation and lower plasma folate concentrations were significantly more likely to have higher BMI, % BF or WC (OR = 2.49, 95% CI:1.41-4.47, P = 0.002; OR = 2.49, 95% CI:1.40-4.51, P = 0.002 and OR = 1.98, 95% = 1.14-3.48 P = 0.0145, respectively) and higher HOMA-IR (OR = 1.78, 95% CI:1.02-3.13, P = 0.041).

CONCLUSION

Our results demonstrated that a lower degree of PBMC L1 methylation is associated with excess body weight and higher HOMA-IR, especially in the presence of lower concentrations of plasma folate.

Epigenetics and aging

Over the past two decades, a growing interest on the research of the biological basis of human longevity has emerged, in order to clarify the intricacy of biological and environmental factors affecting (together with stochastic factors) the quality and the rate of human aging. These researches have outlined a complex scenario in which epigenetic marks, such as DNA methylation and numerous histone modifications, are emerging as important factors of the overall variation in life expectancy. In fact, epigenetic marks, that are responsible of the establishment of specific expression programs and of genome stability, represent a "drawbridge" across genetic, environmental and stochastic factors. In this review we provide an overview on the current knowledge and the general features of the epigenetic modifications characterizing the aging process.

Interindividual variability and co-regulation of DNA methylation differ among blood cell populations

DNA methylation regulates gene expression in a cell-type specific way. Although peripheral blood mononuclear cells (PBMCs) comprise a heterogeneous cell population, most studies of DNA methylation in blood are performed on total mononuclear cells. In this study, we investigated high resolution methylation profiles of 58 CpG sites dispersed over eight immune response genes in multiple purified blood cells from healthy adults and newborns. Adjacent CpG sites showed methylation levels that were increasingly correlated in adult blood vs. cord blood. Thus, while interindividual variability increases from newborn to adult blood, the underlying methylation changes may not be merely stochastic, but seem to be orchestrated as clusters of adjacent CpG sites. Multiple linear regression analysis showed that interindividual methylation variability was influenced by distance of average methylation levels to the closest border (0 or 100%), presence of transcription factor binding sites, CpG conservation across species and age. Furthermore, CD4+ and CD14+ cell types were negative predictors of methylation variability. Concerns that PBMC methylation differences may be confounded by variations in blood cell composition were justified for CpG sites with large methylation differences across cell types, such as in the IFN-γ gene promoter. Taken together, our data suggest that unsorted mononuclear cells are reasonable surrogates of CD8+ and, to a lesser extent, CD4+ T cell methylation in adult peripheral, but not in neonatal, cord blood.

Alu and LINE-1 methylation and lung function in the normative ageing study

OBJECTIVES

To investigate the association between methylation of transposable elements Alu and long-interspersed nuclear elements (LINE-1) and lung function.

DESIGN

Cohort study.

SETTING

Outpatient Veterans Administration facilities in greater Boston, Massachusetts, USA.

PARTICIPANTS

Individuals from the Veterans Administration Normative Aging Study, a longitudinal study of aging in men, evaluated between 1999 and 2007. The majority (97%) were white.

PRIMARY AND SECONDARY OUTCOME MEASURES

Primary predictor was methylation, assessed using PCR-pyrosequencing after bisulphite treatment. Primary outcome was lung function as assessed by spirometry, performed according to American Thoracic Society/European Respiratory Society guidelines at the same visit as the blood draws.

RESULTS

In multivariable models adjusted for age, height, body mass index (BMI), pack-years of smoking, current smoking and race, Alu hypomethylation was associated with lower forced expiratory volume in 1 s (FEV(1)) (β=28 ml per 1% change in Alu methylation, p=0.017) and showed a trend towards association with a lower forced vital capacity (FVC) (β=27 ml, p=0.06) and lower FEV(1)/FVC (β=0.3%, p=0.058). In multivariable models adjusted for age, height, BMI, pack-years of smoking, current smoking, per cent lymphocytes, race and baseline lung function, LINE-1 hypomethylation was associated with more rapid decline of FEV(1) (β=6.9 ml/year per 1% change in LINE-1 methylation, p=0.005) and of FVC (β=9.6 ml/year, p=0.002).

CONCLUSIONS

In multiple regression analysis, Alu hypomethylation was associated with lower lung function, and LINE-1 hypomethylation was associated with more rapid lung function decline in a cohort of older and primarily white men from North America. Future studies should aim to replicate these findings and determine if Alu or LINE-1 hypomethylation may be due to specific and modifiable environmental exposures.

Patterns and possible roles of LINE-1 methylation changes in smoke-exposed epithelia

Tobacco smoking and reduced methylation of long interspersed element-1 (LINE-1) are crucial in oral carcinogenesis. 5'UTR of human LINE-1 sequence contains several CpG dinucleotides which are methylated in various proportions (0-100%). Methylation levels of many LINE-1s in cancer were reduced, hypomethylated. The hypomethylation of each LINE-1 locus can promote instability of genome and repress expression of a gene located on that same chromosome. This study investigated if cigarette smoking influences LINE-1 methylation of oral mucosal cells. The methylation of human LINE-1 in clinically normal oral mucosa of current smokers was compared to non-smokers. By using the combined bisulphite restriction analysis, each LINE-1 sequence was categorised into 4 patterns depending on the methylation status and location of the two 18-bp successive CpG from 5' to 3' including (m)C(m)C, (u)C(u)C, (m)C(u)C and (u)C(m)C. Of these, (m)C and (u)C represent methylated and unmethylated CpG, respectively. The DNA bisulphite sequence demonstrated that most CpGs of (m)C(m)C and (u)C(u)C were methylated and unmethylated, respectively. Nevertheless, some CpGs of each (m)C(u)C or (u)C(m)C allele were methylated. Imaging of the digestion products was used to generate %methylation value. No significant difference in the overall LINE-1 methylation level but the differences in percentages of some methylation patterns were discovered. The %(m)C(m)C and %(u)C(u)C increased, while the %(m)C(u)C decreased in current smokers (p = 0.002, 0.015, and <0.0001, respectively). Additionally, the lower %(m)C(u)C still persisted in persons who had stopped smoking for over 1 year (p = 0.001). The %(m)C(u)C also decreased in the higher pack-year smokers (p = 0.028). Smoking possibly altered (m)C(u)C to (m)C(m)C and (u)C(u)C forms, and changes (u)C(m)C to (u)C(u)C forms. In conclusion, smoking changes methylation levels of partial methylated LINE-1s and increased the number of hypo- and hypermethylated loci. These hypomethylated LINE-1s may possess carcinogenesis potential. Moreover, LINE-1 methylation patterns may be useful for monitoring oral carcinogenesis in smokers.

Global LINE-1 DNA methylation is associated with blood glycaemic and lipid profiles

Background Patterns of DNA methylation change with age and these changes are believed to be associated with the development of common complex diseases. The hypothesis that Long Interspersed Nucleotide Element 1 (LINE-1) DNA methylation (an index of global DNA methylation) is associated with biomarkers of metabolic health was investigated in this study.

Methods Global LINE-1 DNA methylation was quantified by pyrosequencing in blood-derived DNA samples from 228 individuals, aged 49–51 years, from the Newcastle Thousand Families Study (NTFS). Associations between log-transformed LINE-1 DNA methylation levels and anthropometric and blood biochemical measurements, including triglycerides, total cholesterol, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol, fasting glucose and insulin secretion and resistance were examined.

Results Linear regression, after adjustment for sex, demonstrated positive associations between log-transformed LINE-1 DNA methylation and fasting glucose {coefficient 2.80 [95% confidence interval (CI) 0.39–5.22]}, total cholesterol [4.76 (95% CI 1.43–8.10)], triglycerides [3.83 (95% CI 1.30–6.37)] and LDL-cholesterol [5.38 (95% CI 2.12–8.64)] concentrations. A negative association was observed between log-transformed LINE-1 methylation and both HDL cholesterol concentration [−1.43 (95% CI −2.38 to −0.48)] and HDL:LDL ratio [−1.06 (95% CI −1.76 to −0.36)]. These coefficients reflect the millimoles per litre change in biochemical measurements per unit increase in log-transformed LINE-1 methylation.

Conclusions These novel associations between global LINE-1 DNA methylation and blood glycaemic and lipid profiles highlight a potential role for epigenetic biomarkers as predictors of metabolic disease and may be relevant to future diagnosis, prevention and treatment of this group of disorders. Further work is required to establish the role of confounding and reverse causation in the observed associations.

Distinct DNA methylomes of newborns and centenarians

Human aging cannot be fully understood in terms of the constrained genetic setting. Epigenetic drift is an alternative means of explaining age-associated alterations. To address this issue, we performed whole-genome bisulfite sequencing (WGBS) of newborn and centenarian genomes. The centenarian DNA had a lower DNA methylation content and a reduced correlation in the methylation status of neighboring cytosine--phosphate--guanine (CpGs) throughout the genome in comparison with the more homogeneously methylated newborn DNA. The more hypomethylated CpGs observed in the centenarian DNA compared with the neonate covered all genomic compartments, such as promoters, exonic, intronic, and intergenic regions. For regulatory regions, the most hypomethylated sequences in the centenarian DNA were present mainly at CpG-poor promoters and in tissue-specific genes, whereas a greater level of DNA methylation was observed in CpG island promoters. We extended the study to a larger cohort of newborn and nonagenarian samples using a 450,000 CpG-site DNA methylation microarray that reinforced the observation of more hypomethylated DNA sequences in the advanced age group. WGBS and 450,000 analyses of middle-age individuals demonstrated DNA methylomes in the crossroad between the newborn and the nonagenarian/centenarian groups. Our study constitutes a unique DNA methylation analysis of the extreme points of human life at a single-nucleotide resolution level.

LINE-1 methylation status and its association with tetralogy of fallot in infants

Background

Methylation levels of long interspersed nucleotide elements (LINE-1) are representative of genome-wide methylation status and play an important role in maintaining genomic stability and gene expression. To derive insight into the association between genome-wide methylation status and tetralogy of fallot (TOF), we compared the methylation status of LINE-1 element between TOF patients and controls. The methylation of the NKX 2–5, HAND 1, and TBX 20 promoter regions was also evaluated.

Methods

Genomic DNA from right ventricular tissue samples was obtained from 32 patients with TOF and 15 control subjects. Sequenom MassARRAY platform was performed to examine the methylation levels of LINE-1, NKX2-5, HAND1 and TBX20. Mann–Whitney U test was used to compare differences in methylation levels between two groups.

Results

The methylation level of LINE-1 was significantly lower in patients with TOF, with a median of 57.95% (interquartile range [IQR]: 56.10%–60.04%), as opposed to 59.70% in controls (IQR: 59.00%–61.30%; P = 0.0021). The highest LINE-1 methylation level was 61.3%. The risk of TOF increased in subjects with the lowest methylation levels (less than or equal to 59.0%; OR = 14.7, 95% CI: 1.8–117.7, P = 0.014) and in those with medium methylation levels (59.0%–61.3%; OR = 2.0, 95% CI: 0.3–14.2, P = 0.65). An ROC curve analysis showed a relatively high accuracy of using the LINE-1 methylation level in predicting the presence of TOF (AUC = 0.78, 95% CI: 0.65–0.91; P = 0.002). The association of the LINE-1 methylation level with TOF was only observed in males (P = 0.006) and not in females (P = 0.25). Neither age nor gender was found to be associated with the LINE-1 methylation level in patients or controls. Higher methylation levels of NKX2-5 and HAND1 and lower methylation levels of TBX20 were also observed in patients with TOF than in controls. No association was found between the methylation levels of NKX2-5, HAND1 and TBX 20 with the LINE-1 methylation level.

Conclusions

Lower LINE-1 methylation levels are associated with increased risk of TOF and may provide important clues for the development of TOF.

Plasticity of DNA methylation in mouse T cell activation and differentiation

Background

Circulating CD4⁺ T helper cells are activated through interactions with antigen presenting cells and undergo differentiation into specific T helper cell subsets depending on the type of antigen encountered. In addition, the relative composition of the circulating CD4⁺ T cell population changes as animals mature with an increased percentage of the population being memory/effector type cells.

Results

Here, we report on the highly plastic nature of DNA methylation at the genome-wide level as T cells undergo activation, differentiation and aging. Of particular note were the findings that DNA demethylation occurred rapidly following T cell activation and that all differentiated T cell populations displayed lower levels of global methylation than the non-differentiated population. In addition, T cells from older mice had a reduced level of DNA methylation, most likely explained by the increase in the memory/effector cell fraction. Although significant genome-wide changes were observed, changes in DNA methylation at individual genes were restricted to specific cell types. Changes in the expression of enzymes involved in DNA methylation and demethylation reflect in most cases the changes observed in the genome-wide DNA methylation status.

Conclusion

We have demonstrated that DNA methylation is dynamic and flexible in CD4+ T cells and changes rapidly both in a genome-wide and in a targeted manner during T cell activation, differentiation. These changes are accompanied by parallel changes in the enzymatic complexes that have been implicated in DNA methylation and demethylation implying that the balance between these opposing activities may play a role in the maintaining the methylation profile of a given cell type but also allow flexibility in a cell population that needs to respond rapidly to environmental signals.

In utero exposures, infant growth, and DNA methylation of repetitive elements and developmentally related genes in human placenta

BACKGROUND

Fetal programming describes the theory linking environmental conditions during embryonic and fetal development with risk of diseases later in life. Environmental insults in utero may lead to changes in epigenetic mechanisms potentially affecting fetal development.

OBJECTIVES

We examined associations between in utero exposures, infant growth, and methylation of repetitive elements and gene-associated DNA in human term placenta tissue samples.

METHODS

Placental tissues and associated demographic and clinical data were obtained from subjects delivering at Women and Infants Hospital in Providence, Rhode Island (USA). Methylation levels of long interspersed nuclear element-1 (LINE-1) and the Alu element AluYb8 were determined in 380 placental samples from term deliveries using bisulfite pyrosequencing. Genomewide DNA methylation profiles were obtained in a subset of 184 samples using the Illumina Infinium HumanMethylation27 BeadArray. Multiple linear regression, model-based clustering methods, and gene set enrichment analysis examined the association between birth weight percentile, demographic variables, and repetitive element methylation and gene-associated CpG locus methylation.

RESULTS

LINE-1 and AluYb8 methylation levels were found to be significantly positively associated with birth weight percentile (p = 0.01 and p < 0.0001, respectively) and were found to differ significantly among infants exposed to tobacco smoke and alcohol. Increased placental AluYb8 methylation was positively associated with average methylation among CpG loci found in polycomb group target genes; developmentally related transcription factor binding sites were overrepresented for differentially methylated loci associated with both elements.

CONCLUSIONS

Our results suggest that repetitive element methylation markers, most notably AluYb8 methylation, may be susceptible to epigenetic alterations resulting from the intrauterine environment and play a critical role in mediating placenta function, and may ultimately inform on the developmental basis of health and disease.

ALU and LINE-1 hypomethylations in multistep gastric carcinogenesis and their prognostic implications

Focal CpG island hypermethylation and diffuse genomic hypomethylation signify the changes in the DNA methylation status in cancer cells. ALU and LINE-1 repetitive DNA elements comprise ~28% of the human genome. PCR-based measurements of these repetitive DNA elements can be used as a surrogate marker of the genomewide methylation content. Our study aimed to identify the timing of ALU and LINE-1 hypomethylations during multistep gastric carcinogenesis and their prognostic implications in gastric cancer (GC). In our study, we analyzed the methylation statuses of ALU and LINE-1 in 249 cases of gastric biopsy samples and another independent set of 198 cases of advanced GC by pyrosequencing. Regardless of the Helicobacter pylori infection status, a significant decrease in the ALU methylation levels was noted during the transitions from chronic gastritis to intestinal metaplasia and from gastric adenoma to GC. LINE-1 methylation decreased during the transition from intestinal metaplasia to gastric adenoma and no further decrease occurred during the transition from gastric adenoma to GC. A low LINE-1 methylation status was strongly associated with poor prognosis in GC. A multivariate analysis revealed that LINE-1 methylation status was an independent prognostic factor. Our findings suggest that ALU and LINE-1 hypomethylations are early events during multistep gastric carcinogenesis. Furthermore, the LINE-1 methylation status can be used as a molecular biomarker to define a subset of GC patients with poor prognosis.

Aging and epigenetics: longitudinal changes in gene-specific DNA methylation

DNA methylation has been associated with age-related disease. Intra-individual changes in gene-specific DNA methylation over time in a community-based cohort has not been well described. We estimated the change in DNA methylation due to aging for nine genes in an elderly, community-dwelling cohort of men. Seven hundred and eighty four men from the Veterans Administration Normative Aging Study who were living in metropolitan Boston from 1999-2009 donated a blood sample for DNA methylation analysis at clinical examinations repeated at approximately 3-5 year intervals. We used mixed effects regression models. Aging was significantly associated with decreased methylation of GCR, iNOS and TLR2 and with increased methylation of IFNγ, F3, CRAT and OGG. Obstructive pulmonary disease at baseline modified the effect of aging on methylation of IFNγ (interaction p = 0.04). For participants who had obstructive pulmonary disease at their baseline visit, the rate of change of methylation of IFNγ was -0.05% 5-methyl-cytosine (5-mC) per year (95% CI: -0.22, 0.13), but was 0.14% 5-mC per year (95% CI: 0.05, 0.24) for those without this condition. Models with random slopes indicated significant heterogeneity in the effect of aging on methylation of GCR, iNOS and OGG. These findings suggest that DNA methylation may reflect differential biological aging.

Dietary and lifestyle factors of DNA methylation

Lifestyle factors, such as diet, smoking, physical activity, and body weight management, are known to constitute the majority of cancer causes. Epigenetics has been widely proposed as a main mechanism that mediates the reversible effects of dietary and lifestyle factors on carcinogenesis. This chapter reviews human studies on potential dietary and lifestyle determinants of DNA methylation. Apart from a few prospective investigations and interventions of limited size and duration, evidence mostly comes from cross-sectional observational studies and supports some associations. Studies to date suggest that certain dietary components may alter genomic and gene-specific DNA methylation levels in systemic and target tissues, affecting genomic stability and transcription of tumor suppressors and oncogenes. Most data and supportive evidence exist for folate, a key nutritional factor in one-carbon metabolism that supplies the methyl units for DNA methylation. Other candidate bioactive food components include alcohol and other key nutritional factors of one-carbon metabolism, polyphenols and flavonoids in green tea, phytoestrogen, and lycopene. Some data also support a link of DNA methylation with physical activity and energy balance. Effects of dietary and lifestyle exposures on DNA methylation may be additionally modified by common genetic variants, environmental carcinogens, and infectious agents, an aspect that remains largely unexplored. In addition, growing literature supports that the environmental conditions during critical developmental stages may influence later risk of metabolic disorders in part through persistent programming of DNA methylation. Further research of these modifiable determinants of DNA methylation will improve our understanding of cancer etiology and may present certain DNA methylation markers as attractive surrogate endpoints for prevention research. Considering the plasticity of epigenetic marks and correlated nature of lifestyle factors, more longitudinal studies of healthy individuals of varying age, sex, and ethnic groups are warranted, ideally with comprehensive data collection on various lifestyle factors.

A refined, rapid and reproducible high resolution melt (HRM)-based method suitable for quantification of global LINE-1 repetitive element methylation

Background

The methylation of DNA is recognized as a key mechanism in the regulation of genomic stability and evidence for its role in the development of cancer is accumulating. LINE-1 methylation status represents a surrogate measure of genome-wide methylation.

Findings

Using high resolution melt (HRM) curve analysis technology, we have established an in-tube assay that is linear (r > 0.9986) with a high amplification efficiency (90-105%), capable of discriminating between partcipant samples with small differences in methylation, and suitable for quantifying a wide range of LINE-1 methylation levels (0-100%)--including the biologically relevant range of 50-90% expected in human DNA. We have optimized this procedure to perform using 2 μg of starting DNA and 2 ng of bisulfite-converted DNA for each PCR reaction. Intra- and inter-assay coefficients of variation were 1.44% and 0.49%, respectively, supporting the high reproducibility and precision of this approach.

Conclusions

In summary, this is a completely linear, quantitative HRM PCR method developed for the measurement of LINE-1 methylation. This cost-efficient, refined and reproducible assay can be performed using minimal amounts of starting DNA. These features make our assay suitable for high throughput analysis of multiple samples from large population-based studies.

Blood leukocyte Alu and LINE-1 methylation and gastric cancer risk in the Shanghai Women's Health Study

Background:

Recent data suggest a link between blood leukocyte DNA methylation, and cancer risk. However, reports on DNA methylation from a prospective study are unavailable for gastric cancer.

Methods:

We explored the association between methylation in pre-diagnostic blood leukocyte DNA and gastric cancer risk in a case–control study nested in the prospective Shanghai Women's Health Study cohort. Incident gastric cancer cases (n=192) and matched controls (n=384) were included in the study. Methylation of Alu and long interspersed nucleotide elements (LINE)-1 were evaluated using bisulphite pyrosequencing. Odds ratios (ORs) and 95% confidence intervals (CI) were calculated from logistic regression adjusting for potential confounders.

Results:

Alu methylation was inversely associated with gastric cancer risk, mainly among cases diagnosed one or more years after blood collection. After excluding cases diagnosed during the first year of follow-up, the ORs for the third, second, and first quartiles of Alu methylation compared with the highest quartile were 2.43 (1.43–4.13), 1.47(0.85–2.57), and 2.22 (1.28–3.84), respectively. This association appeared to be modified by dietary intake, particularly isoflavone. In contrast, LINE-1 methylation levels were not associated with gastric cancer risk.

Conclusion:

Evidence from this prospective study is consistent with the hypothesis that DNA hypomethylation in blood leukocytes may be related to cancer risk, including risk of gastric cancer.

LINE-1 methylation levels in leukocyte DNA and risk of renal cell cancer

Purpose

Leukocyte global DNA methylation levels are currently being considered as biomarkers of cancer susceptibility and have been associated with risk of several cancers. In this study, we aimed to examine the association between long interspersed nuclear elements (LINE-1) methylation levels, as a biomarker of global DNA methylation in blood cell DNA, and renal cell cancer risk.

Experimental Design

LINE-1 methylation of bisulfite-converted genomic DNA isolated from leukocytes was quantified by pyrosequencing measured in triplicate, and averaged across 4 CpG sites. A total of 328 RCC cases and 654 controls frequency-matched(2∶1) on age(±5years), sex and study center, from a large case-control study conducted in Central and Eastern Europe were evaluated.

Results

LINE-1 methylation levels were significantly higher in RCC cases with a median of 81.97% (interquartile range[IQR]: 80.84–83.47) compared to 81.67% (IQR: 80.35–83.03) among controls (p = 0.003, Wilcoxon). Compared to the lowest LINE-1 methylation quartile(Q1), the adjusted ORs for increasing methylation quartiles were as follows: OR(Q2) = 1.84(1.20−2.81), OR(Q3) = 1.72(1.11−2.65) and OR(Q4) = 2.06(1.34−3.17), with a p-trend = 0.004. The association was stronger among current smokers (p-trend<0.001) than former or never smokers (p-interaction = 0.03). To eliminate the possibility of selection bias among controls, the relationship between LINE-1 methylation and smoking was evaluated and confirmed in a case-only analysis, as well.

Conclusions

Higher levels of LINE-1 methylation appear to be positively associated with RCC risk, particularly among current smokers. Further investigations using both post- and pre-diagnostic genomic DNA is warranted to confirm findings and will be necessary to determine whether the observed differences occur prior to, or as a result of carcinogenesis.

Global methylation in exposure biology and translational medical science

BACKGROUND

Many groups are actively investigating how the epigenetic state relates to environmental exposures and development of disease, including cancer. There are myriad choices for capturing and measuring the epigenetic state of a tissue, ranging from assessing the total methyl-CpG content to array-based platforms that simultaneously probe hundreds of thousands of CpG loci. There is an emerging literature that uses CpG methylation at repetitive sequences, including LINE-1 (long interspersed nuclear element-1) elements, to capture the epigenomic state.

OBJECTIVES

We explored the complexity of using CpG methylation at repetitive sequences in epidemiology and translational medical research and suggest needed avenues of research to clarify its meaning and utility.

CONCLUSIONS

Among the most urgent avenues of research is the need for prospective studies to eliminate the possibilities of reverse causality, and development of new LINE-1 assays that capture both class of LINE-1 element and copy number.

Transcriptional repression of repeat-derived transcripts correlates with histone hypoacetylation at repetitive DNA elements in aged mice brain

In order to better characterize epigenetic alterations at repetitive DNA elements with aging, DNA methylation and histone marks at various repeat classes were investigated. Repetitive DNA elements were hypermethylated in the brains of old mice. Histone hypoacetylation and altered histone trimethylation at repetitive sequences were detected in brain tissues during aging. The expression of repeat-derived transcripts (RDTs) was then measured to explore any correlations with the observed epigenetic alterations. Large numbers of RDTs investigated were down-regulated along with age. Bisulfite sequencing revealed that CpG dinucleotide methylation patterns at the repeats of the RDT promoter region were mostly well maintained during aging. ChIP assay showed that histones were deacetylated at the promoter region of RDTs in aged mice brain. The observations indicate that the transcriptional repression of RDTs appears to be related to histone hypoacetylation, but not to DNA hypermethylation at repeat DNA elements in the brains of aged mice.

The influence of aging, environmental exposures and local sequence features on the variation of DNA methylation in blood

In order to properly comprehend the epigenetic dysregulation that occurs during the course of disease, there is a need to characterize the epigenetic variability in healthy individuals that arises in response to aging and exposures, and to understand such variation within the biological context of the DNA sequence. We analyzed the methylation of 26,486 autosomal CpG loci in blood from 205 healthy subjects, using three complementary approaches to assess the association between methylation, age or exposures, and local sequence features, such as CpG island status, repeat sequences, location within a polycomb target gene or proximity to a transcription factor binding site. We clustered CpGs (1) using unsupervised recursively partitioned mixture modeling (RPMM) and (2) bioinformatically-informed methods, and (3) also employed a marginal model-based (non-clustering) approach. We observed associations between age and methylation and hair dye use and methylation, where the direction and magnitude was contingent on the local sequence features of the CpGs. Our results demonstrate that CpGs are differentially methylated dependent upon the genomic features of the sequence in which they are embedded, and that CpG methylation is associated with age and hair dye use in a CpG context-dependent manner in healthy individuals.

DNA methylation in neurodegenerative disorders: a missing link between genome and environment?

The risk of developing neurodegenerative disorders such as Alzheimer's disease or Parkinson's disease is influenced by genetic and environmental factors. Environmental events occurring during development or later in life can be related to disease susceptibility. One way by which the environment may exert its effect is through epigenetic modifications, which might affect the functioning of genes. These include nucleosome positioning, post-translational histone modifications, and DNA methylation. In this review we will focus in the potential role of DNA methylation in neurodegenerative disorders and in the approaches to explore such epigenetic changes. Advances in deciphering the role of epigenetic modifications in phenotype are being uncovered for a variety of diseases, including cancer, autoimmune, neurodevelopmental and cognitive disorders. Epigenetic modifications are now being also associated with cardiovascular and metabolic traits, and they are expected to be especially involved in learning and memory processes, as well as in neurodegenerative disease. The study of the role of methylation and other epigenetic modifications in disease development will provide new insights in the etiopathogenesis of neurodegenerative disorders, and should hopefully shape new avenues in the development of therapeutic strategies.

Global hypomethylation identifies Loci targeted for hypermethylation in head and neck cancer

PURPOSE

The human epigenome is profoundly altered in cancers, with a characteristic loss of methylation in repetitive regions and concomitant accumulation of gene promoter methylation. The degree to which these processes are coordinated is unclear so we investigated both in head and neck squamous cell carcinomas.

EXPERIMENTAL DESIGN

Global methylation was measured using the luminometric methylation assay (LUMA) and pyrosequencing of LINE-1Hs and AluYb8 repetitive elements in a series of 138 tumors. We also measured methylation of more than 27,000 CpG loci with the Illumina HumanMethylation27 Microarray (n = 91).

RESULTS

LINE-1 methylation was significantly associated with LUMA and Infinium loci methylation (Spearman's ρ = 0.52/ρ = 0.56, both P < 0.001) but not that of AluYb8. Methylation of LINE-1, AluYb8, and Infinium loci differed by tumor site (each Kruskal-Wallis, P < 0.05). Also, LINE-1 and LUMA methylation were associated with HPV16 E6 serology (each Mann-Whitney, P < 0.05). Comparing LINE-1 methylation to gene-associated methylation, we identified a distinct subset of CpG loci with significant hypermethylation associated with LINE-1 hypomethylation. An investigation of sequence features for these CpG loci revealed that they were significantly less likely to reside in repetitive elements (Gene Set Enrichment Analysis, P < 0.02), enriched in CpG islands (P < 0.001) and were proximal to transcription factor-binding sites (P < 0.05). We validated the top CpG loci that had significant hypermethylation associated with LINE-1 hypomethylation (at EVI2A, IFRD1, KLHL6, and PTPRCAP) by pyrosequencing independent tumors.

CONCLUSIONS

These data indicate that global hypomethylation and gene-specific methylation processes are associated in a sequence-dependent manner, and that clinical characteristics and exposures leading to HNSCC may be influencing these processes.

Long interspersed nuclear element-1 hypomethylation in cancer: biology and clinical applications

Epigenetic changes in long interspersed nuclear element-1s (LINE-1s or L1s) occur early during the process of carcinogenesis. A lower methylation level (hypomethylation) of LINE-1 is common in most cancers, and the methylation level is further decreased in more advanced cancers. Consequently, several previous studies have suggested the use of LINE-1 hypomethylation levels in cancer screening, risk assessment, tumor staging, and prognostic prediction. Epigenomic changes are complex, and global hypomethylation influences LINE-1s in a generalized fashion. However, the methylation levels of some loci are dependent on their locations. The consequences of LINE-1 hypomethylation are genomic instability and alteration of gene expression. There are several mechanisms that promote both of these consequences in cis. Therefore, the methylation levels of different sets of LINE-1s may represent certain phenotypes. Furthermore, the methylation levels of specific sets of LINE-1s may indicate carcinogenesis-dependent hypomethylation. LINE-1 methylation pattern analysis can classify LINE-1s into one of three classes based on the number of methylated CpG dinucleotides. These classes include hypermethylation, partial methylation, and hypomethylation. The number of partial and hypermethylated loci, but not hypomethylated LINE-1s, is different among normal cell types. Consequently, the number of hypomethylated loci is a more promising marker than methylation level in the detection of cancer DNA. Further genome-wide studies to measure the methylation level of each LINE-1 locus may improve PCR-based methylation analysis to allow for a more specific and sensitive detection of cancer DNA or for an analysis of certain cancer phenotypes.

Hypomethylation of LINE-1 but not Alu in lymphocyte subsets of systemic lupus erythematosus patients

BACKGROUND

T lymphocytes from SLE patients have a global decrease in the 5-methylcytosine content. Previous studies have identified hypomethylation in the promoter of several genes but there is limited study in the interspersed repetitive sequences (IRSs).

METHODS

We examined and compared the methylation levels of long interspersed nuclear element 1s (LINE-1) and Alu elements in normal and SLE CD4+ T lymphocytes, CD8+ T lymphocytes and B lymphocytes by the combined bisulfite restriction analysis-interspersed repetitive sequences (COBRA-IRS).

RESULTS

Hypomethylation of LINE-1 but not Alu was found in CD4+ T lymphocytes, CD8+ T lymphocytes, and B lymphocytes of SLE patient (P=0.005, 0.002, and 0.007, respectively). Moreover, when the SLE patients were divided into active and inactive groups, LINE-1 hypomethylation was more significantly distinguished in both CD4+ and CD8+ T lymphocytes of patients from the active SLE group when compared to the controls. Surprisingly, Alu hypomethylation was also observed in CD8+ T lymphocytes from the inactive SLE group when compared to the normal controls (P=0.0056).

CONCLUSIONS

The hypomethylation in each lymphocyte subset of SLE was IRSs specific, mainly found in LINE-1 rather than Alu.

Age-associated increase in heterochromatic marks in murine and primate tissues

Chromatin is highly dynamic and subject to extensive remodeling under many physiologic conditions. Changes in chromatin that occur during the aging process are poorly documented and understood in higher organisms, such as mammals. We developed an immunofluorescence assay to quantitatively detect, at the single cell level, changes in the nuclear content of chromatin-associated proteins. We found increased levels of the heterochromatin-associated proteins histone macro H2A (mH2A) and heterochromatin protein 1 beta (HP1β) in human fibroblasts during replicative senescence in culture, and for the first time, an age-associated increase in these heterochromatin marks in several tissues of mice and primates. Mouse lung was characterized by monophasic mH2A expression histograms at both ages, and an increase in mean staining intensity at old age. In the mouse liver, we observed increased age-associated localization of mH2A to regions of pericentromeric heterochromatin. In the skeletal muscle, we found two populations of cells with either low or high mH2A levels. This pattern of expression was similar in mouse and baboon, and showed a clear increase in the proportion of nuclei with high mH2A levels in older animals. The frequencies of cells displaying evidence of increased heterochromatinization are too high to be readily accounted for by replicative or oncogene-induced cellular senescence, and are prominently found in terminally differentiated, postmitotic tissues that are not conventionally thought to be susceptible to senescence. Our findings distinguish specific chromatin states in individual cells of mammalian tissues, and provide a foundation to investigate further the progressive epigenetic changes that occur during aging.

Recent insights into regulation of transcription by RNA polymerase III and the cellular functions of its transcripts

The products of transcription by the multisubunit enzyme RNA polymerase III (Pol III), such as 5S rRNA, tRNAs, U6 snRNA, are important for cell growth, proliferation and differentiation. The known range of the Pol III transcriptome has expanded over recent years, and novel functions of the newly discovered and already well known transcripts have been identified, including regulation of stress responses and apoptosis. Furthermore, transcription by Pol III has turned out to be strongly regulated, differing between diverse class III genes, among cell types and under stress conditions. The mechanisms involved in regulation of Pol III transcription are being elucidated and disturbances in that regulation have been implicated in various diseases, including cancer. This review summarizes the novel data on the regulation of RNA polymerase III transcription, including epigenetic and gene specific mechanisms and outlines recent insights into the cellular functions of the Pol III transcriptome, in particular of SINE RNAs.

Hypomethylation of intragenic LINE-1 represses transcription in cancer cells through AGO2

In human cancers, the methylation of long interspersed nuclear element -1 (LINE-1 or L1) retrotransposons is reduced. This occurs within the context of genome wide hypomethylation, and although it is common, its role is poorly understood. L1s are widely distributed both inside and outside of genes, intragenic and intergenic, respectively. Interestingly, the insertion of active full-length L1 sequences into host gene introns disrupts gene expression. Here, we evaluated if intragenic L1 hypomethylation influences their host gene expression in cancer. First, we extracted data from L1base (http://l1base.molgen.mpg.de), a database containing putatively active L1 insertions, and compared intragenic and intergenic L1 characters. We found that intragenic L1 sequences have been conserved across evolutionary time with respect to transcriptional activity and CpG dinucleotide sites for mammalian DNA methylation. Then, we compared regulated mRNA levels of cells from two different experiments available from Gene Expression Omnibus (GEO), a database repository of high throughput gene expression data, (http://www.ncbi.nlm.nih.gov/geo) by chi-square. The odds ratio of down-regulated genes between demethylated normal bronchial epithelium and lung cancer was high (p<1E⁻²⁷; OR = 3.14; 95% CI = 2.54–3.88), suggesting cancer genome wide hypomethylation down-regulating gene expression. Comprehensive analysis between L1 locations and gene expression showed that expression of genes containing L1s had a significantly higher likelihood to be repressed in cancer and hypomethylated normal cells. In contrast, many mRNAs derived from genes containing L1s are elevated in Argonaute 2 (AGO2 or EIF2C2)-depleted cells. Hypomethylated L1s increase L1 mRNA levels. Finally, we found that AGO2 targets intronic L1 pre-mRNA complexes and represses cancer genes. These findings represent one of the mechanisms of cancer genome wide hypomethylation altering gene expression. Hypomethylated intragenic L1s are a nuclear siRNA mediated cis-regulatory element that can repress genes. This epigenetic regulation of retrotransposons likely influences many aspects of genomic biology.

Specific age-associated DNA methylation changes in human dermal fibroblasts

Epigenetic modifications of cytosine residues in the DNA play a critical role for cellular differentiation and potentially also for aging. In mesenchymal stromal cells (MSC) from human bone marrow we have previously demonstrated age-associated methylation changes at specific CpG-sites of developmental genes. In continuation of this work, we have now isolated human dermal fibroblasts from young (<23 years) and elderly donors (>60 years) for comparison of their DNA methylation profiles using the Infinium HumanMethylation27 assay. In contrast to MSC, fibroblasts could not be induced towards adipogenic, osteogenic and chondrogenic lineage and this is reflected by highly significant differences between the two cell types: 766 CpG sites were hyper-methylated and 752 CpG sites were hypo-methylated in fibroblasts in comparison to MSC. Strikingly, global DNA methylation profiles of fibroblasts from the same dermal region clustered closely together indicating that fibroblasts maintain positional memory even after in vitro culture. 75 CpG sites were more than 15% differentially methylated in fibroblasts upon aging. Very high hyper-methylation was observed in the aged group within the INK4A/ARF/INK4b locus and this was validated by pyrosequencing. Age-associated DNA methylation changes were related in fibroblasts and MSC but they were often regulated in opposite directions between the two cell types. In contrast, long-term culture associated changes were very consistent in fibroblasts and MSC. Epigenetic modifications at specific CpG sites support the notion that aging represents a coordinated developmental mechanism that seems to be regulated in a cell type specific manner.

DNA ploidy, nuclear size, proliferation index and DNA-hypomethylation in ovarian cancer

OBJECTIVE

The present study was undertaken to analyze the impact of epigenetic alterations with a main focus on nuclear area, aneuploidy, hyperploidy, and proliferation in 70 ovarian cancer specimens.

METHODS

Morphometric changes and somatic chromosomal ploidy status were assessed by Feulgen spectrophotometry. DNA-hypomethylation of LINE1 repeats was analyzed by means of MethyLight PCR, and methylation levels of satellite 2 (Sat2) and satellite alpha (Satα) DNA sequences in chromosome 1 were measured by Southern blot analysis. These parameters were analyzed with regard to correlations as well as to recurrence and survival.

RESULTS

We identified a significant association between LINE1 DNA-hypomethylation and patient age (p=0.029). Furthermore, LINE1 DNA-hypomethylation was positively correlated with the nuclear area (r=0.47; p<0.001) and the proliferation index (r=0.36; p<0.001). Univariate survival analysis showed that the nuclear area and LINE1 DNA-hypomethylation were prognostic factors for overall (p=0.015 and =0.006, respectively) and progression-free survival (p=0.020 and p=0.001 respectively), the percentage of aneuploidy only for overall survival (p=0.031). Subgroup survival analyses revealed that the prognostic value of these factors is strictly confined to mucinous cancers. In serous cancers no prognostic value could be pointed out for any analyzed parameter. Multivariate analysis of the entire cohort showed that the percentage of hyperploidy was an independent prognostic parameter for overall survival (p=0.003) and LINE1 DNA-hypomethylation for progression-free survival (p=0.03). In mucinous cancers nuclear area and LINE1 DNA-hypomethylation were found to be independent predictors of progression-free and overall survival.

CONCLUSIONS

In this study we identified the correlations between early cancer-associated genome DNA-hypomethylation, nuclear morphometric changes, somatic chromosomal ploidy status and the proliferation index. Prognostic relevance of nuclear area and LINE1 DNA-hypomethylation was revealed exclusively in mucinous ovarian cancers.

Methylation at global LINE-1 repeats in human blood are affected by gender but not by age or natural hormone cycles

Previously, we reported on inter-individual and gender specific variations of LINE-1 methylation in healthy individuals. In this study, we investigated whether this variability could be influenced by age or sex hormones in humans. To this end, we studied LINE-1 methylation in vivo in blood-derived DNA from individuals aged 18 to 64 years and from young healthy females at various hormone levels during the menstrual cycle. Our results show that no significant association with age was observed. However, the previously reported increase of LINE-1 methylation in males was reconfirmed. In females, although no correlation between LINE-1 or Alu methylation and hormone levels was observed, a significant stable individual specific level of methylation was noted. In vitro results largely confirmed these findings, as neither estrogen nor dihydrotestosterone affected LINE-1 or Alu methylation in Hek293T, HUVEC, or MDA-kb2 cell lines. In contrast, a decrease in methylation was observed in estrogen-treated T47-Kbluc cell lines strongly expressing estrogen receptor. The very low expression of estrogen receptor in blood cells could explain the observed insensitivity of methylation at LINE-1 to natural hormonal variations in females. In conclusion, neither natural cycle of hormones nor age has a detectable effect on the LINE-1 methylation in peripheral blood cells, while gender remains an important factor.

Epigenetics of early child development

Comprehensive clinical studies show that adverse conditions in early life can severely impact the developing brain and increase vulnerability to mood disorders later in life. During early postnatal life the brain exhibits high plasticity which allows environmental signals to alter the trajectories of rapidly developing circuits. Adversity in early life is able to shape the experience-dependent maturation of stress-regulating pathways underlying emotional functions and endocrine responses to stress, such as the hypothalamo-pituitary-adrenal (HPA) system, leading to long-lasting altered stress responsivity during adulthood. To date, the study of gene-environment interactions in the human population has been dominated by epidemiology. However, recent research in the neuroscience field is now advancing clinical studies by addressing specifically the mechanisms by which gene-environment interactions can predispose individuals toward psychopathology. To this end, appropriate animal models are being developed in which early environmental factors can be manipulated in a controlled manner. Here we will review recent studies performed with the common aim of understanding the effects of the early environment in shaping brain development and discuss the newly developing role of epigenetic mechanisms in translating early life conditions into long-lasting changes in gene expression underpinning brain functions. Particularly, we argue that epigenetic mechanisms can mediate the gene-environment dialog in early life and give rise to persistent epigenetic programming of adult physiology and dysfunction eventually resulting in disease. Understanding how early life experiences can give rise to lasting epigenetic marks conferring increased risk for mental disorders, how they are maintained and how they could be reversed, is increasingly becoming a focus of modern psychiatry and should pave new guidelines for timely therapeutic interventions.

HERV-K hypomethylation in ovarian clear cell carcinoma is associated with a poor prognosis and platinum resistance

INTRODUCTION

In general, ovarian clear cell carcinoma (OCCC) has a history of poor response to standard platinum-based chemotherapy regimens, and advanced cases have short survival periods. Therefore, the discovery of a biomarker for the pretreatment prediction of OCCC is crucial. Loss of methylation of a retrotransposable sequence, such as long interspersed repetitive sequence 1 (LINE-1), frequently occurs in cancers, including ovarian cancer, and it has been proven to be associated with poor survival. The expressions of human endogenous retrovirus (HERV) K and E were found to be increased in tissues from patients with OCCC. Here, we propose that methylation levels of HERV are associated with treatment response and prognosis of OCCC.

METHODS

Twenty-nine patients with OCCC were enrolled. Methylation levels of HERV-K, HERV-E, and LINE-1 were measured from microdissected cancer and normal ovarian tissues. The methylation levels were correlated with stage, treatment response, and prognosis.

RESULTS

Methylation levels of HERV-K, HERV-E, and LINE-1 were decreased in tissues from patients with advanced stage cancer (P = 0.0179, P = 0.0021, and P = 0.0307, respectively). Human endogenous retrovirus K demonstrated significantly lower methylation levels in the platinum-resistant group (P = 0.0004). Patients with lower levels of methylated (hypomethylated) HERV-K had a shorter mean overall survival (P = 0.006). In advanced OCCC cases, patients with hypomethylated HERV-K had shorter mean progression-free survival (P = 0.018) and mean overall survival (P = 0.018) than did patients with higher methylation levels of HERV-K.

CONCLUSIONS

Methylation levels of HERV-K, HERV-E, and LINE-1 are decreased during OCCC multistep carcinogenesis. Moreover, HERV-K hypomethylation is a promising biomarker for predicting OCCC treatment response and prognosis.

Chromatin: a molecular interface between cancer and aging

To prevent cancer, mammals have evolved potent tumor suppression mechanisms, including senescence and apoptosis. These processes depend on regulation of chromatin. Chromatin-dependent tumor suppressor pathways are activated in premalignant cells and tissues harboring cancer-causing genetic alterations, and also in normal aged tissue, the latter likely due to accumulation of genetic and cellular damage. Paradoxically, however, disruption of chromatin structure may also promote cancer. Apparent defects in chromatin structure accumulate with age, the biggest single risk factor for cancer. Evidence suggests that these age-associated perturbations in chromatin structure contribute to the age-associated increase in incidence of cancer. Thus, alterations in chromatin structure can both suppress and promote the onset of cancer, and both activities are inextricably linked to aging.

Correlation of global and gene-specific DNA methylation in maternal-infant pairs

The inheritance of DNA methylation patterns is a popular theory to explain the influence of parental genetic and environmental factors on the phenotype of their offspring but few studies have examined this relationship in humans. Using 120 paired maternal-umbilical cord blood samples randomly selected from a prospective birth cohort in Bangladesh, we quantified DNA methylation by pyrosequencing seven CpG positions in the promoter region of p16, four CpG positions in the promoter region of p53, LINE-1 and Alu. Positive correlations were observed between maternal and umbilical cord blood at p16, LINE-1, and Alu but not p53. Multiple linear regression models observed a significant association between maternal and umbilical cord blood at LINE-1 and Alu (LINE-1: β = 0.63, p<0.0001; Alu: β = 0.28, p = 0.009). After adjusting for multiple comparisons, maternal methylation of p16 at position 4 significantly predicted methylation at the same position in umbilical cord blood (β = 0.43, p = <0.0001). These models explained 48%, 5% and 16% of the observed variability in umbilical cord %5mC for LINE-1, Alu and p16 at position 4, respectively. These results suggest that DNA methylation in maternal blood was correlated with her offspring at LINE-1, Alu, and p16 but not p53. Additional studies are needed to confirm whether these observed associations were due to the inheritance of epigenetic events or the shared environment between mother and fetus. Future studies should also use a multi-generational family-based design that would quantify both maternal and paternal contributions to DNA methylation in offspring across more than one generation.

The Janus face of DNA methylation in aging

Aging is arguably the most familiar yet least-well understood aspect of human biology. The role of epigenetics in aging and age-related diseases has gained interest given recent advances in the understanding of how epigenetic mechanisms mediate the interactions between the environment and the genetic blueprint. While current concepts generally view global deteriorations of epigenetic marks to insidiously impair cellular and molecular functions, an active role for epigenetic changes in aging has so far received little attention. In this regard, we have recently shown that early-life adversity induced specific changes in DNA methylation that were protected from an age-associated erasure and correlated with a phenotype well-known to increase the risk for age-related mental disorders. This finding strengthens the idea that DNA (de-)methylation is controlled by multiple mechanisms that might fulfill different, and partly contrasting, roles in the aging process.