Induction of altered epigenetic regulation of the hepatic glucocorticoid receptor in the offspring of rats fed a protein-restricted diet during pregnancy suggests that reduced DNA methyltransferase-1 expression is involved in impaired DNA methylation and changes in histone modifications

Early-life adversity programs emotional functions and the neuroendocrine stress system: the contribution of nutrition, metabolic hormones and epigenetic mechanisms

Clinical and pre-clinical studies have shown that early-life adversities, such as abuse or neglect, can increase the vulnerability to develop psychopathologies and cognitive decline later in life. Remarkably, the lasting consequences of stress during this sensitive period on the hypothalamic-pituitary-adrenal axis and emotional function closely resemble the long-term effects of early malnutrition and suggest a possible common pathway mediating these effects. During early-life, brain development is affected by both exogenous factors, like nutrition and maternal care as well as by endogenous modulators including stress hormones. These elements, while mostly considered for their independent actions, clearly do not act alone but rather in a synergistic manner. In order to better understand how the programming by early-life stress takes place, it is important to gain further insight into the exact interplay of these key elements, the possible common pathways as well as the underlying molecular mechanisms that mediate their effects. We here review evidence that exposure to both early-life stress and early-life under-/malnutrition similarly lead to life-long alterations on the neuroendocrine stress system and modify emotional functions. We further discuss how the different key elements of the early-life environment interact and affect one another and next suggest a possible role for the early-life adversity induced alterations in metabolic hormones and nutrient availability in shaping later stress responses and emotional function throughout life, possibly via epigenetic mechanisms. Such knowledge will help to develop intervention strategies, which gives the advantage of viewing the synergistic action of a more complete set of changes induced by early-life adversity.

Fetal and childhood growth patterns associated with bone mass in school-age children: the Generation R Study

Low birth weight is associated with lower bone accrual in children and peak bone mass in adults. We assessed how different patterns of longitudinal fetal and early childhood growth influence bone properties at school age. In 5431 children participating in a population-based prospective cohort study, we measured fetal growth by ultrasound at 20 and 30 weeks gestation, and childhood growth at birth, 1, 2, 3, and 4 years of age. We analyzed these growth measurements in relation to total body (less head) BMD measured by DXA at age 6. We used conditional growth modeling; a technique which takes into account correlation between repeatedly measured growth measures. Our results showed that estimated fetal weight gain, femur length growth between 20 and 30 weeks of gestation, femur length growth between 30 weeks and birth, as well as all height and weight growth measurements from birth to 4 years of age were all positively associated with BMC, bone area (BA), and BMD (all p < 0.01). Fetal femur length growth between 30 weeks and birth was positively associated with BMC and BA (both p < 0.001), but not with BMD. Overall, childhood growth measurements exerted a larger influence on bone measures than fetal growth measures. The strongest effect estimate was observed during the first year of life. Children born small (<10th percentile) for gestational age (SGA) had lower BMC and BA, but not BMD, than children born appropriate for gestational age (AGA), whereas children born large (>90th percentile) for gestational age (LGA) had higher BMC and BA (all p < 0.001). These differences were no longer present in children showing subsequent accelerated and decelerated infant growth, respectively. We conclude that both fetal and childhood growth patterns are associated with bone mineral accrual, showing the strongest effect estimates in infancy. Compensatory infant growth counteracts the adverse consequences of fetal growth restriction on bone development.

Obesity-related hypertension: possible pathophysiological mechanisms

Hypertension is one of the major risk factors of cardiovascular diseases, but despite a century of clinical and basic research, the discrete etiology of this disease is still not fully understood. The same is true for obesity, which is recognized as a major global epidemic health problem nowadays. Obesity is associated with an increasing prevalence of the metabolic syndrome, a cluster of risk factors including hypertension, abdominal obesity, dyslipidemia, and hyperglycemia. Epidemiological studies have shown that excess weight gain predicts future development of hypertension, and the relationship between BMI and blood pressure (BP) appears to be almost linear in different populations. There is no doubt that obesity-related hypertension is a multifactorial and polygenic trait, and multiple potential pathogenetic mechanisms probably contribute to the development of higher BP in obese humans. These include hyperinsulinemia, activation of the renin-angiotensin-aldosterone system, sympathetic nervous system stimulation, abnormal levels of certain adipokines such as leptin, or cytokines acting at the vascular endothelial level. Moreover, some genetic and epigenetic mechanisms are also in play. Although the full manifestation of both hypertension and obesity occurs predominantly in adulthood, their roots can be traced back to early ontogeny. The detailed knowledge of alterations occurring in the organism of experimental animals during particular critical periods (developmental windows) could help to solve this phenomenon in humans and might facilitate the age-specific prevention of human obesity-related hypertension. In addition, better understanding of particular pathophysiological mechanisms might be useful in so-called personalized medicine.

Regulation of early human growth: impact on long-term health

Growth and development are central characteristics of childhood. Deviations from normal growth can indicate serious health challenges. The adverse impact of early growth faltering and malnutrition on later health has long been known. In contrast, the impact of rapid early weight and body fat gain on programming of later disease risk have only recently received increased attention. Numerous observational studies related diet in early childhood and rapid early growth to the risk of later obesity and associated disorders. Causality was confirmed in a large, double-blind randomised trial testing the 'Early Protein Hypothesis'. In this trial we found that attenuation of protein supply in infancy normalized early growth and markedly reduced obesity prevalence in early school age. These results indicate the need to describe and analyse growth patterns and their regulation through diet in more detail and to characterize the underlying metabolic and epigenetic mechanisms, given the potential major relevance for public health and policy. Better understanding of growth patterns and their regulation could have major benefits for the promotion of public health, consumer-orientated nutrition recommendations, and the development of improved food products for specific target populations.

Paternal influences on offspring development: behavioural and epigenetic pathways

Although mammalian parent-offspring interactions during early life are primarily through the mother, there is increasing evidence for the impact of fathers on offspring development. A critical issue concerns the pathways through which this paternal influence is achieved. In the present review, we highlight the literature suggesting several of these routes of paternal effects in mammals. First, similar to mothers, fathers can influence offspring development through the direct care of offspring, as has been observed in biparental species. Second, there is growing evidence that, even in the absence of contact with offspring, fathers can transmit environmentally-induced effects (i.e. behavioural, neurobiological and metabolic phenotypes induced by stress, nutrition and toxins) to offspring and it has been speculated that these effects are achieved through inherited epigenetic variation within the patriline. Third, fathers may also impact the quality of mother-infant interactions and thus achieve an indirect influence on offspring. Importantly, these pathways of paternal influence are not mutually exclusive but rather serve as an illustration of the complex mechanisms through which parental influence is achieved. These influences may serve to transmit traits across generations, thus leading to a transgenerational transmission of neurobiological and behavioural phenotypes.

Osteoporosis: a lifecourse approach

It is becoming increasingly apparent that the risk of developing osteoporosis is accrued throughout the entire lifecourse, even from as early as conception. Thus early growth is associated with bone mass at peak and in older age, and risk of hip fracture. Novel findings from mother-offspring cohorts have yielded greater understanding of relationships between patterns of intrauterine and postnatal growth in the context of later bone development. Study of biological samples from these populations has helped characterize potential mechanistic underpinnings, such as epigenetic processes. Global policy has recognized the importance of early growth and nutrition to the risk of developing adult chronic noncommunicable diseases such as osteoporosis; testing of pregnancy interventions aimed at optimizing offspring bone health is now underway. It is hoped that through such programs, novel public health strategies may be established with the ultimate goal of reducing the burden of osteoporotic fracture in older age.

Epigenetic reprogramming in breast cancer: from new targets to new therapies

Breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer death among women in the United States. Recently, interest has grown in the role of epigenetics in breast cancer development and progression. Epigenetic changes such as DNA methylation, histone modifications, and abnormal expression of non-coding RNAs emerged as novel biomarkers in breast cancer diagnosis, therapy, and prevention. This review focuses on the most recent mechanistic findings underlying epigenetic changes in breast cancer development and their role as predictors of breast cancer risk. The rapid progress in our understanding of epigenetic findings in breast cancer has opened new avenues for potential therapeutic approaches via identification of epigenetic targets. We highlight the development of novel epigenetically targeted drugs, relevant clinical trials in breast cancer patients, and recent approaches combining epigenetic agents with chemotherapy and/or endocrine therapy that may incrementally improve long-term outcomes in appropriately selected breast cancer patients. Biomarkers of response are needed, however, to identify patient subsets that are most likely to benefit from epigenetic treatment strategies.

The genetics of diabetic pregnancy

Advancements in molecular technology coupled with a greater awareness of the human genome and epigenome have broadened our understanding of the genetic contributions to the diabetic pregnancy. There are multiple genes and pathways that can result in a hyperglycemic environment for the fetus. Exposure to this environment in utero has an impact on the risk of adult-onset chronic diseases. How identification of an individual's genetic variants will impact clinical care and outcomes will continue to evolve as our understanding grows.

A conceptual framework for the developmental origins of health and disease

In the last decades, the developmental origins of health and disease (DOHaD) have emerged as a vigorous field combining experimental, clinical, epidemiological and public health research. Its goal is to understand how events in early life shape later morbidity risk, especially of non-communicable chronic diseases. As these diseases become the major cause of morbidity and mortality worldwide, research arising from DOHaD is likely to gain significance to public health and economic development. But action may be hindered by the lack of a firm mechanistic explanation and of a conceptual basis, especially regarding the evolutionary significance of the DOHaD phenomenon. In this article, we provide a succinct historical review of the research into the relationship between development and later disease, consider the evolutionary and developmental significance and discuss the underlying mechanisms of the DOHaD phenomenon. DOHaD should be viewed as a part of a broader biological mechanism of plasticity by which organisms, in response to cues such as nutrition or hormones, adapt their phenotype to environment. These responses may be divided into those for immediate benefit and those aimed at prediction of a future environment: disease occurs in the mismatch between predicted and realized future. The likely mechanisms that enable plasticity involve epigenetic processes, affecting the expression of genes associated with regulatory pathways. There is now evidence that epigenetic marks may be inherited and so contribute to non-genomic heritable disease risk. We end by discussing the global significance of the DOHaD phenomenon and its potential applications for public health purposes.

Nutritional influences on epigenetic programming: asthma, allergy, and obesity

Observational studies show consistent links between early-life nutritional exposures as important risk factors for the development of asthma, allergy, and obesity. Reliance on increasing use of dietary supplementation and fortification (eg, with folate) to compensate for increased consumption of processed foods is also influencing immune and metabolic outcomes. Epigenetics is providing substantial advances in understanding how early-life nutritional exposures can effect disease development. This article summarizes current evidence linking the influence of early-life nutritional exposures on epigenetic regulation with a focus on the disease outcomes of asthma, allergy, and obesity.

Epigenetic changes in hypothalamic appetite regulatory genes may underlie the developmental programming for obesity in rat neonates subjected to a high-carbohydrate dietary modification

Earlier, we showed that rearing of newborn rats on a high-carbohydrate (HC) milk formula resulted in the onset of hyperinsulinemia, its persistence in the post-weaning period and adult-onset obesity. DNA methylation of CpG dinucleotides in the proximal promoter region and modifications in the N-terminal tail of histone 3 associated with the neuropeptide Y (Npy) and pro-opiomelanocortin (Pomc) genes were investigated to decipher the molecular mechanisms supporting the development of obesity in HC females. Although there were no differences in the methylation status of CpG dinucleotides in the proximal promoter region of the Pomc gene, altered methylation of specific CpG dinucleotides proximal to the transcription start site was observed for the Npy gene in the hypothalami of 16- and 100-day-old HC rats compared with their methylation status in mother-fed (MF) rats. Investigation of histone tail modifications on hypothalamic chromatin extracts from 16-day-old rats indicated decreased acetylation of lysine 9 in histone 3 (H3K9) for the Pomc gene and increased acetylation for the same residue for the Npy gene, without changes in histone methylation (H3K9) in both genes in HC rats. These findings are consistent with the changes in the levels of Npy and Pomc mRNAs in the hypothalami of HC rats compared with MF animals. Our results suggest that epigenetic modifications could contribute to the altered gene expression of the Npy and Pomc genes in the hypothalami of HC rats and could be a mechanism leading to hyperphagia and the development of obesity in adult female HC rats.

Metabolic syndrome components are associated with DNA hypomethylation

BACKGROUND

Disturbances of DNA methylation have been associated with multiple diseases, including cardiovascular disease, cancer and, as some have suggested, glucometabolic disturbances. Our aim was to assess the association of the metabolic syndrome and its individual components with DNA methylation in a population-based study.

MATERIALS AND METHODS

In a human population (n = 738) stratified by age, sex and glucose metabolism, we explored associations of the metabolic syndrome according to National Cholesterol Education Program/Adult Treatment Panel-III criteria and its individual components (fasting glucose, high-density lipoprotein cholesterol, triglycerides, blood pressure, waist circumference) with global leukocyte DNA methylation. DNA methylation was measured as the methylcytosine/cytosine ratio in peripheral leukocytes using liquid chromatography-tandem mass spectrometry.

RESULTS

Individuals with the metabolic syndrome had relative DNA hypomethylation compared to participants without the syndrome (β = -0.05; p = 0.01). This association was mainly attributable to linear associations of two metabolic syndrome components with DNA methylation: fasting plasma glucose (β = -0.02; p = 0.004) and high-density lipoprotein cholesterol (β = 0.07; p = 0.004). People with type 2 diabetes or impaired glucose metabolism had DNA hypomethylation compared to normoglycemic individuals (β = -0.05; p = 0.004).

CONCLUSIONS

DNA hypomethylation is independently associated with hyperglycemia and low high-density lipoprotein cholesterol, both essential components of the metabolic syndrome. The potential implications and direction of possible causality require further study.

Early-life nutritional programming of longevity

Available data from both experimental and epidemiological studies suggest that inadequate diet in early life can permanently change the structure and function of specific organs or homoeostatic pathways, thereby ‘programming’ the individual’s health status and longevity. Sufficient evidence has accumulated showing significant impact of epigenetic regulation mechanisms in nutritional programming phenomenon. The essential role of early-life diet in the development of aging-related chronic diseases is well established and described in many scientific publications. However, the programming effects on lifespan have not been extensively reviewed systematically. The aim of the review is to provide a summary of research findings and theoretical explanations that indicate that longevity can be influenced by early nutrition.

Early life nutrition, epigenetics and programming of later life disease

The global pandemic of obesity and type 2 diabetes is often causally linked to marked changes in diet and lifestyle; namely marked increases in dietary intakes of high energy diets and concomitant reductions in physical activity levels. However, less attention has been paid to the role of developmental plasticity and alterations in phenotypic outcomes resulting from altered environmental conditions during the early life period. Human and experimental animal studies have highlighted the link between alterations in the early life environment and increased risk of obesity and metabolic disorders in later life. This link is conceptualised as the developmental programming hypothesis whereby environmental influences during critical periods of developmental plasticity can elicit lifelong effects on the health and well-being of the offspring. In particular, the nutritional environment in which the fetus or infant develops influences the risk of metabolic disorders in offspring. The late onset of such diseases in response to earlier transient experiences has led to the suggestion that developmental programming may have an epigenetic component, as epigenetic marks such as DNA methylation or histone tail modifications could provide a persistent memory of earlier nutritional states. Moreover, evidence exists, at least from animal models, that such epigenetic programming should be viewed as a transgenerational phenomenon. However, the mechanisms by which early environmental insults can have long-term effects on offspring are relatively unclear. Thus far, these mechanisms include permanent structural changes to the organ caused by suboptimal levels of an important factor during a critical developmental period, changes in gene expression caused by epigenetic modifications (including DNA methylation, histone modification, and microRNA) and permanent changes in cellular ageing. A better understanding of the epigenetic basis of developmental programming and how these effects may be transmitted across generations is essential for the implementation of initiatives aimed at curbing the current obesity and diabetes crisis.

Genome-wide quantitative analysis of histone H3 lysine 4 trimethylation in wild house mouse liver: environmental change causes epigenetic plasticity

In mammals, exposure to toxic or disease-causing environments can change epigenetic marks that are inherited independently of the intrauterine environment. Such inheritance of molecular phenotypes may be adaptive. However, studies demonstrating molecular evidence for epigenetic inheritance have so far relied on extreme treatments, and are confined to inbred animals. We therefore investigated whether epigenomic changes could be detected after a non-drastic change in the environment of an outbred organism. We kept two populations of wild-caught house mice (Mus musculus domesticus) for several generations in semi-natural enclosures on either standard diet and light cycle, or on an energy-enriched diet with longer daylight to simulate summer. As epigenetic marker for active chromatin we quantified genome-wide histone-3 lysine-4 trimethylation (H3K4me3) from liver samples by chromatin immunoprecipitation and high-throughput sequencing as well as by quantitative polymerase chain reaction. The treatment caused a significant increase of H3K4me3 at metabolic genes such as lipid and cholesterol regulators, monooxygenases, and a bile acid transporter. In addition, genes involved in immune processes, cell cycle, and transcription and translation processes were also differently marked. When we transferred young mice of both populations to cages and bred them under standard conditions, most of the H3K4me3 differences were lost. The few loci with stable H3K4me3 changes did not cluster in metabolic functional categories. This is, to our knowledge, the first quantitative study of an epigenetic marker in an outbred mammalian organism. We demonstrate genome-wide epigenetic plasticity in response to a realistic environmental stimulus. In contrast to disease models, the bulk of the epigenomic changes we observed were not heritable.

Exercise prevents maternal high-fat diet-induced hypermethylation of the Pgc-1α gene and age-dependent metabolic dysfunction in the offspring

Abnormal conditions during early development adversely affect later health. We investigated whether maternal exercise could protect offspring from adverse effects of a maternal high-fat diet (HFD) with a focus on the metabolic outcomes and epigenetic regulation of the metabolic master regulator, peroxisome proliferator-activated receptor γ coactivator-1α (Pgc-1α). Female C57BL/6 mice were exposed to normal chow, an HFD, or an HFD with voluntary wheel exercise for 6 weeks before and throughout pregnancy. Methylation of the Pgc-1α promoter at CpG site -260 and expression of Pgc-1α mRNA were assessed in skeletal muscle from neonatal and 12-month-old offspring, and glucose and insulin tolerance tests were performed in the female offspring at 6, 9, and 12 months. Hypermethylation of the Pgc-1α promoter caused by a maternal HFD was detected at birth and was maintained until 12 months of age with a trend of reduced expression of Pgc-1α mRNA (P = 0.065) and its target genes. Maternal exercise prevented maternal HFD-induced Pgc-1α hypermethylation and enhanced Pgc-1α and its target gene expression, concurrent with amelioration of age-associated metabolic dysfunction at 9 months of age in the offspring. Therefore, maternal exercise is a powerful lifestyle intervention for preventing maternal HFD-induced epigenetic and metabolic dysregulation in the offspring.

Differential pathways to adult metabolic dysfunction following poor nutrition at two critical developmental periods in sheep

Epidemiological and experimental studies suggest early nutrition has long-term effects on susceptibility to obesity, cardiovascular and metabolic diseases. Small and large animal models confirm the influence of different windows of sensitivity, from fetal to early postnatal life, on offspring phenotype. We showed previously that undernutrition in sheep either during the first month of gestation or immediately after weaning induces differential, sex-specific changes in adult metabolic and cardiovascular systems. The current study aims to determine metabolic and molecular changes that underlie differences in lipid and glucose metabolism induced by undernutrition during specific developmental periods in male and female sheep. Ewes received 100% (C) or 50% nutritional requirements (U) from 1–31 days gestation, and 100% thereafter. From weaning (12 weeks) to 25 weeks, offspring were then fed either ad libitum (CC, UC) or were undernourished (CU, UU) to reduce body weight to 85% of their individual target. From 25 weeks, all offspring were fed ad libitum. A cohort of late gestation fetuses were studied after receiving either 40% nutritional requirements (1–31 days gestation) or 50% nutritional requirements (104–127 days gestation). Post-weaning undernutrition increased in vivo insulin sensitivity, insulin receptor and glucose transporter 4 expression in muscle, and lowered hepatic methylation at the delta-like homolog 1/maternally expressed gene 3 imprinted cluster in adult females, but not males. Early gestational undernutrition induced lower hepatic expression of gluconeogenic factors in fetuses and reduced in vivo adipose tissue insulin sensitivity in adulthood. In males, undernutrition in early gestation increased adipose tissue lipid handling mechanisms (lipoprotein lipase, glucocorticoid receptor expression) and hepatic methylation within the imprinted control region of insulin-like growth factor 2 receptor in adulthood. Therefore, undernutrition during development induces changes in mechanisms of lipid and glucose metabolism which differ between tissues and sexes dependent on the period of nutritional restriction. Such changes may increase later life obesity and dyslipidaemia risk.

Childhood bone mineral content is associated with methylation status of the RXRA promoter at birth

Maternal vitamin D deficiency has been associated with reduced offspring bone mineral accrual. Retinoid-X receptor-alpha (RXRA) is an essential cofactor in the action of 1,25-dihydroxyvitamin D (1,25[OH]2 -vitamin D), and RXRA methylation in umbilical cord DNA has been associated with later offspring adiposity. We tested the hypothesis that RXRA methylation in umbilical cord DNA collected at birth is associated with offspring skeletal development, assessed by dual-energy X-ray absorptiometry, in a population-based mother-offspring cohort (Southampton Women's Survey). Relationships between maternal plasma 25-hydroxyvitamin D (25[OH]-vitamin D) concentrations and cord RXRA methylation were also investigated. In 230 children aged 4 years, a higher percent methylation at four of six RXRA CpG sites measured was correlated with lower offspring bone mineral content (BMC) corrected for body size (β = -2.1 to -3.4 g/SD, p = 0.002 to 0.047). In a second independent cohort (n = 64), similar negative associations at two of these CpG sites, but positive associations at the two remaining sites, were observed; however, none of the relationships in this replication cohort achieved statistical significance. The maternal free 25(OH)-vitamin D index was negatively associated with methylation at one of these RXRA CpG sites (β = -3.3 SD/unit, p = 0.03). Thus, perinatal epigenetic marking at the RXRA promoter region in umbilical cord was inversely associated with offspring size-corrected BMC in childhood. The potential mechanistic and functional significance of this finding remains a subject for further investigation.

Embryonic exposure to corticosterone modifies aggressive behavior through alterations of the hypothalamic pituitary adrenal axis and the serotonergic system in the chicken

Exposure to excess glucocorticoids (GCs) during embryonic development influences offspring phenotypes and behaviors and induces epigenetic modifications of the genes in the hypothalamic-pituitary-adrenal (HPA) axis and in the serotonergic system in mammals. Whether prenatal corticosterone (CORT) exposure causes similar effects in avian species is less clear. In this study, we injected low (0.2μg) and high (1μg) doses of CORT into developing embryos on day 11 of incubation (E11) and tested the changes in aggressive behavior and hypothalamic gene expression on posthatch chickens of different ages. In ovo administration of high dose CORT significantly suppressed the growth rate from 3weeks of age and increased the frequency of aggressive behaviors, and the dosage was associated with elevated plasma CORT concentrations and significantly downregulated hypothalamic expression of arginine vasotocin (AVT) and corticotropin-releasing hormone (CRH). The hypothalamic content of glucocorticoid receptor (GR) protein was significantly decreased in the high dose group (p<0.05), whereas no changes were observed for GR mRNA. High dose CORT exposure significantly increased platelet serotonin (5-HT) uptake, decreased whole blood 5-HT concentration (p<0.05), downregulated hypothalamic tryptophan hydroxylase 1 (TPH1) mRNA and upregulated 5-HT receptor 1A (5-HTR1A) and monoamine oxidase A (MAO-A) mRNA, but not monoamine oxidase B (MAO-B). High dose CORT also significantly increased DNA methylation of the hypothalamic GR and CRH gene promoters (p<0.05). Our findings suggest that embryonic exposure to CORT programs aggressive behavior in the chicken through alterations of the HPA axis and the serotonergic system, which may involve modifications in DNA methylation.

Early origins of adult disease: approaches for investigating the programmable epigenome in humans, nonhuman primates, and rodents

According to the developmental origins of health and disease hypothesis, in utero experiences reprogram an individual for immediate adaptation to gestational perturbations, with the sequelae of later-in-life risk of metabolic disease. An altered gestational milieu with resultant adult metabolic disease has been observed in instances of both in utero constraint (e.g., from famine or uteroplacental insufficiency) and overt caloric abundance (e.g., from a maternal high-fat, caloric-dense diet). The commonality of the adult metabolic phenotype begs the question of how diverse in utero experiences (i.e., reprogramming events) converge on common metabolic pathways and how the memory of these events is maintained across the lifespan. We and others have investigated the molecular mechanisms underlying fetal programming and observed that epigenetic modifications to the fetal and placental epigenome accompany these reprogramming events. Based on several lines of emerging data in human and nonhuman primates, it is now felt that modified epigenetic signature--and the histone code in particular--underlies alterations in postnatal gene expression and metabolic pathways central to accurate functioning and maintenance of health. Because of the tissue lineage specificity of many of these modifications, nonhuman primates serve as an apt model system for the capacity to recapitulate human gene expression and regulation during development. This review summarizes recent epigenetic advances using rodent and primate (both human and nonhuman) models during in utero development and contributing to adult diseases later in life.

Epigenetic programming and risk: the birthplace of cardiovascular disease?

Epigenetics, through control of gene expression circuitries, plays important roles in various physiological processes such as stem cell differentiation and self renewal. This occurs during embryonic development, in different tissues, and in response to environmental stimuli. The language of epigenetic program is based on specific covalent modifications of DNA and chromatin. Thus, in addition to the individual identity, encoded by sequence of the four bases of the DNA, there is a cell type identity characterized by its positioning in the epigenetic "landscape". Aberrant changes in epigenetic marks induced by environmental cues may contribute to the development of abnormal phenotypes associated with different human diseases such as cancer, neurological disorders and inflammation. Most of the epigenetic studies have focused on embryonic development and cancer biology, while little has been done to explore the role of epigenetic mechanisms in the pathogenesis of cardiovascular disease. This review highlights our current knowledge of epigenetic gene regulation and the evidence that chromatin remodeling and histone modifications play key roles in the pathogenesis of cardiovascular disease through (re)programming of cardiovascular (stem) cells commitment, identity and function.

Environment-physiology, diet quality and energy balance: the influence of early life nutrition on future energy balance

Diseases caused by impaired regulation of energy balance, in particular obesity, represent a major global health burden. Although polymorphisms, lifestyle and dietary choices have been associated with differential risk of obesity and related conditions, a substantial proportion of the variation in disease risk remains unexplained. Evidence from epidemiological studies, natural experiments and from studies in animal models has shown that a poor intra-uterine environment is associated causally with increased risk of obesity and metabolic disease in adulthood. Induction of phenotypes that increase disease risk involves the fetus receiving cues from the mother about the environment which, via developmental plasticity, modify the phenotype of the offspring to match her environment. However, inaccurate information may induce an offspring phenotype that is mismatched to the future environment. Such mismatch has been suggested to underlie increased risk of metabolic disease associated with a poor early life environment. Recent studies have shown that induction of modified phenotypes in the offspring involves altered epigenetic regulation of specific genes. Identification of a central role of epigenetics in the aetiology of obesity and metabolic disease may facilitate the development of novel therapeutic interventions and of biomarkers of disease risk.

Breast cancer and the importance of early life nutrition

Epigenetic processes play a central role in regulating the tissue-specific expression of genes. Alterations in these processes can lead to profound changes in phenotype and have been implicated in the pathogenesis of many human diseases including human cancer. There is growing evidence that the environment, particularly variations in diet, during specific developmental periods can induce changes in the epigenome, which are then stably maintained throughout life influencing susceptibility to cancer in later life. This chapter will review the evidence that alterations in early life nutritional exposure can affect breast cancer risk through the altered epigenetic regulation of genes and discuss how detection of such altered epigenetic marks in early life may provide biomarkers to detect individuals at increased risk of disease.

Genome-wide methylation and gene expression changes in newborn rats following maternal protein restriction and reversal by folic acid

A large body of evidence from human and animal studies demonstrates that the maternal diet during pregnancy can programme physiological and metabolic functions in the developing fetus, effectively determining susceptibility to later disease. The mechanistic basis of such programming is unclear but may involve resetting of epigenetic marks and fetal gene expression. The aim of this study was to evaluate genome-wide DNA methylation and gene expression in the livers of newborn rats exposed to maternal protein restriction. On day one postnatally, there were 618 differentially expressed genes and 1183 differentially methylated regions (FDR 5%). The functional analysis of differentially expressed genes indicated a significant effect on DNA repair/cycle/maintenance functions and of lipid, amino acid metabolism and circadian functions. Enrichment for known biological functions was found to be associated with differentially methylated regions. Moreover, these epigenetically altered regions overlapped genetic loci associated with metabolic and cardiovascular diseases. Both expression changes and DNA methylation changes were largely reversed by supplementing the protein restricted diet with folic acid. Although the epigenetic and gene expression signatures appeared to underpin largely different biological processes, the gene expression profile of DNA methyl transferases was altered, providing a potential link between the two molecular signatures. The data showed that maternal protein restriction is associated with widespread differential gene expression and DNA methylation across the genome, and that folic acid is able to reset both molecular signatures.

Exposure of neonatal rats to maternal cafeteria feeding during suckling alters hepatic gene expression and DNA methylation in the insulin signalling pathway

Nutrition in early life is a determinant of lifelong physiological and metabolic function. Diseases that are associated with ageing may, therefore, have their antecedents in maternal nutrition during pregnancy and lactation. Rat mothers were fed either a standard laboratory chow diet (C) or a cafeteria diet (O) based upon a varied panel of highly palatable human foods, during lactation. Their offspring were then weaned onto chow or cafeteria diet giving four groups of animals (CC, CO, OC, OO n = 9-10). Livers were harvested 10 weeks post-weaning for assessment of gene and protein expression, and DNA methylation. Cafeteria feeding post-weaning impaired glucose tolerance and was associated with sex-specific altered mRNA expression of peroxisome proliferator activated receptor gamma and components of the insulin signalling pathway (Irs2, Akt1 and IrB). Exposure to the cafeteria diet during the suckling period modified the later response to the dietary challenge. Post-weaning cafeteria feeding only down-regulated IrB when associated with cafeteria feeding during suckling (group OO, interaction of diet in weaning and lactation P = 0.041). Responses to cafeteria diet during both phases of the experiment varied between males and females. Global DNA methylation was altered in the liver following cafeteria feeding in the post-weaning period, in males but not females. Methylation of the IrB promoter was increased in group OC, but not OO (P = 0.036). The findings of this study add to a growing evidence base that suggests tissue function across the lifespan a product of cumulative modifications to the epigenome and transcriptome, which may be both tissue and sex-specific.

Maternal undernutrition programs tissue-specific epigenetic changes in the glucocorticoid receptor in adult offspring

Epidemiological data indicate that an adverse maternal environment during pregnancy predisposes offspring to metabolic syndrome with increased obesity, and type 2 diabetes. The mechanisms are still unclear although epigenetic modifications are implicated and the hypothalamus is a likely target. We hypothesized that maternal undernutrition (UN) around conception in sheep would lead to epigenetic changes in hypothalamic neurons regulating energy balance in the offspring, up to 5 years after the maternal insult. We found striking evidence of decreased glucocorticoid receptor (GR) promoter methylation, decreased histone lysine 27 trimethylation, and increased histone H3 lysine 9 acetylation in hypothalami from male and female adult offspring of UN mothers. These findings are entirely compatible with the increased GR mRNA and protein observed in the hypothalami. The increased GR predicted the decreased hypothalamic proopiomelanocortin expression and increased obesity that we observed in the 5-year-old adult males. The epigenetic and expression changes in GR were specific to the hypothalamus. Hippocampal GR mRNA and protein were decreased in UN offspring, whereas pituitary GR was altered in a sex-specific manner. In peripheral polymorphonuclear leukocytes there were no changes in GR methylation or protein, indicating that this epigenetic analysis did not predict changes in the brain. Overall, these results suggest that moderate changes in maternal nutrition, around the time of conception, signal life-long and tissue-specific epigenetic alterations in a key gene regulating energy balance in the hypothalamus.

Prenatal caloric restriction enhances DNA methylation and MeCP2 recruitment with reduced murine placental glucose transporter isoform 3 expression

Diminished transplacental glucose transport plays an important role in prenatal calorie restriction (CR) induced reduction in fetal growth. Fetal growth restriction (FGR) has an impact in shaping the adult phenotype with transgenerational implications. To understand the mechanisms underlying prenatal CR-induced transplacental glucose transport, we examined the epigenetic regulation of placental glucose transporter (Glut1 and Glut3) expression. We restricted calories by 50% in C57BL6 pregnant mice from gestational days 10 to 19 (CR; n=8) vs. controls (CON; n=8) and observed a 50% diminution in placental Glut3 expression (P<.05) with no effect on Glut1 expression by reverse transcription and quantitative real-time polymerase chain reaction (PCR). CR enhanced DNA methylation of a CpG island situated ~1000 bp upstream from the transcriptional start site of the glut3 gene, with no such effect on the glut1 gene as assessed by methylation-sensitive PCR and bisulfite sequencing. Chromatin immunoprecipitation (ChIP) assays demonstrated enhanced MeCP2 binding to the CpG island of the glut3 gene in response to CR vs. CON (P<.05). Sequential ChIP demonstrated that enhanced MeCP2 binding of the glut3-(m)CpG island enhanced histone deacetylase 2 recruitment (P<.05) but interfered with Sp1 binding (P<.001), although it did not affect Sp3 or Creb/pCreb interaction. We conclude that late-gestation CR enhanced DNA methylation of the placental glut3 gene. This epigenetic change augmented specific nuclear protein-DNA complex formation that was associated with prenatal CR-induced reduction of placental glut3 expression and thereby transplacental glucose transport. This molecular complex provides novel targets for developing therapeutic interventions aimed at reversing FGR.

Induction of the hepatic stearoyl-CoA desaturase 1 gene in offspring after isocaloric administration of high fat sucrose diet during gestation

Adverse early nutrition leads to metabolic aberrations in adulthood. Molecular and cellular mechanisms responsible are emerging; specific nutritional causes remain unclarified. We investigated gestational dietary intake and its influences on metabolism in offspring. Three groups of pregnant Sprague-Dawley rats were fed either AIN93G standard diet as control, isocaloric high fat sucrose diet or calorie restriction diet (50% of control) until delivery. All dams were fed control diet ad libitum during lactation. Offsprings’ metabolic parameters were assessed at three weeks. Visceral fat and plasma triglycerides of high fat sucrose diet offspring were significantly higher than those of control diet and calorie restriction diet offspring. Plasma leptin level was higher in high fat sucrose diet than control offspring. Conversely, plasma adiponectin was lower in high fat sucrose diet and calorie restriction diet offspring compared to controls. Significant inductions of hepatic mRNA expression of stearoyl-CoA desaturase1 and Δ-5 desaturase genes, were observed in high fat sucrose diet and calorie restriction diet offspring. Gestational high sugar and fat intake even without over energy intake would be more detrimental to metabolisms of offspring compared to calorie restriction.

Peroxisome proliferator activated receptor α ligands as anticancer drugs targeting mitochondrial metabolism

Tumor cells show metabolic features distinctive from normal tissues, with characteristically enhanced aerobic glycolysis, glutaminolysis and lipid synthesis. Peroxisome proliferator activated receptor α (PPAR α) is activated by nutrients (fatty acids and their derivatives) and influences these metabolic pathways acting antagonistically to oncogenic Akt and c-Myc. Therefore PPAR α can be regarded as a candidate target molecule in supplementary anticancer pharmacotherapy as well as dietary therapeutic approach. This idea is based on hitting the cancer cell metabolic weak points through PPAR α mediated stimulation of mitochondrial fatty acid oxidation and ketogenesis with simultaneous reduction of glucose and glutamine consumption. PPAR α activity is induced by fasting and its molecular consequences overlap with the effects of calorie restriction and ketogenic diet (CRKD). CRKD induces increase of NAD+/NADH ratio and drop in ATP/AMP ratio. The first one is the main stimulus for enhanced protein deacetylase SIRT1 activity; the second one activates AMP-dependent protein kinase (AMPK). Both SIRT1 and AMPK exert their major metabolic activities such as fatty acid oxidation and block of glycolysis and protein, nucleotide and fatty acid synthesis through the effector protein peroxisome proliferator activated receptor gamma 1 α coactivator (PGC-1α). PGC-1α cooperates with PPAR α and their activities might contribute to potential anticancer effects of CRKD, which were reported for various brain tumors. Therefore, PPAR α activation can engage molecular interplay among SIRT1, AMPK, and PGC-1α that provides a new, low toxicity dietary approach supplementing traditional anticancer regimen.

Epigenetics of neural repair following spinal cord injury

Spinal cord injury results from an insult inflicted on the spinal cord that usually encompasses its 4 major functions (motor, sensory, autonomic, and reflex). The type of deficits resulting from spinal cord injury arise from primary insult, but their long-term severity is due to a multitude of pathophysiological processes during the secondary phase of injury. The failure of the mammalian spinal cord to regenerate and repair is often attributed to the very feature that makes the central nervous system special-it becomes so highly specialized to perform higher functions that it cannot effectively reactivate developmental programs to re-build novel circuitry to restore function after injury. Added to this is an extensive gliotic and immune response that is essential for clearance of cellular debris, but also lays down many obstacles that are detrimental to regeneration. Here, we discuss how the mature chromatin state of different central nervous system cells (neural, glial, and immune) may contribute to secondary pathophysiology, and how restoring silenced developmental gene expression by altering histone acetylation could stall secondary damage and contribute to novel approaches to stimulate endogenous repair.

Role of epigenetics in Rett syndrome

Rett syndrome (RTT) is an X-linked neurodevelopmental disease caused by MECP2 mutations. The MeCP2 protein was originally thought to function as a transcription repressor by binding to methylated CpG dinucleotides, but is now also thought to be a transcription activator. Recent studies suggest that MeCP2 is not only being expressed in neurons, but also in glial cells, which suggests a new paradigm for understanding the pathogenesis of RTT. It has also been demonstrated that reintroduction of MeCP2 into behaviorally affected Mecp2-null mice after birth rescues neurological symptoms, which indicates that epigenetic failures in RTT are reversible. Therefore, RTT may well be seen as a model disease that can be potentially treated by taking advantage of the reversibility of epigenetic phenomena in various congenital neurodevelopmental diseases that were previously thought to be untreatable.

Nutritional models of foetal programming and nutrigenomic and epigenomic dysregulations of fatty acid metabolism in the liver and heart

Barker's concept of 'foetal programming' proposes that intrauterine growth restriction (IUGR) predicts complex metabolic diseases through relationships that may be further modified by the postnatal environment. Dietary restriction and deficit in methyl donors, folate, vitamin B12, and choline are used as experimental conditions of foetal programming as they lead to IUGR and decreased birth weight. Overfeeding and deficit in methyl donors increase central fat mass and lead to a dramatic increase of plasma free fatty acids (FFA) in offspring. Conversely, supplementing the mothers under protein restriction with folic acid reverses metabolic and epigenomic phenotypes of offspring. High-fat diet or methyl donor deficiency (MDD) during pregnancy and lactation produce liver steatosis and myocardium hypertrophy that result from increased import of FFA and impaired fatty acid β-oxidation, respectively. The underlying molecular mechanisms show dysregulations related with similar decreased expression and activity of sirtuin 1 (SIRT1) and hyperacetylation of peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α). High-fat diet and overfeeding impair AMPK-dependent phosphorylation of PGC-1α, while MDD decreases PGC-1α methylation through decreased expression of PRMT1 and cellular level of S-adenosyl methionine. The visceral manifestations of metabolic syndrome are under the influence of endoplasmic reticulum (ER) stress in overnourished animal models. These mechanisms should also deserve attention in the foetal programming effects of MDD since vitamin B12 influences ER stress through impaired SIRT1 deacetylation of HSF1. Taken together, similarities and synergies of high-fat diet and MDD suggest, therefore, considering their consecutive or contemporary influence in the mechanisms of complex metabolic diseases.

Postweaning exposure to a high-fat diet is associated with alterations to the hepatic histone code in Japanese macaques

BACKGROUND

Expression of circadian gene, Npas2, is altered in fetal life with maternal high-fat (HF) diet exposure by virtue of alterations in the fetal histone code. We postulated that these disruptions would persist postnatally.

METHODS

Pregnant macaques were fed a control (CTR) or HF diet and delivered at term. When offspring were weaned, they were placed on either CTR or HF diet for a period of 5 mo to yield four exposure models (in utero diet/postweaning diet: CTR/CTR n = 5; CTR/HF n = 4; HF/CTR n = 4; and HF/HF n = 5). Liver specimens were obtained at necropsy at 1 y of age.

RESULTS

Hepatic trimethylation of lysine 4 of histone H3 is decreased (CTR/HF 0.87-fold, P = 0.038; HF/CTR 0.84-fold, P = 0.038), whereas hepatic methyltransferase activity increased by virtue of diet exposure (HF/HF 1.3-fold, P = 0.019). Using chromatin immunoprecipitation to determine Npas2 promoter occupancy, we found alterations of both repressive and permissive histone modifications specifically with postweaning HF diet exposure.

CONCLUSION

We found that altered Npas2 expression corresponds with a change in the histone code within the Npas2 promoter.

Perinatal programming of adult hippocampal structure and function; emerging roles of stress, nutrition and epigenetics

Early-life stress lastingly affects adult cognition and increases vulnerability to psychopathology, but the underlying mechanisms remain elusive. In this Opinion article, we propose that early nutritional input together with stress hormones and sensory stimuli from the mother during the perinatal period act synergistically to program the adult brain, possibly via epigenetic mechanisms. We hypothesize that stress during gestation or lactation affects the intake of macro- and micronutrients, including dietary methyl donors, and/or impairs the dam's metabolism, thereby altering nutrient composition and intake by the offspring. In turn, this may persistently modulate gene expression via epigenetic programming, thus altering hippocampal structure and cognition. Understanding how the combination of stress, nutrition, and epigenetics shapes the adult brain is essential for effective therapies.

Effect of prenatal programming on heifer development

In beef cattle, the main factors influencing nutrient partitioning between the dam and fetus include age of the dam, number of fetuses, production demand, and environmental stress. These factors play a critical role in programming the fetus for its future environment and available resources. Fetal programming reportedly affects neonatal mortality and morbidity, postnatal growth rate, body composition, health, and reproduction. Two main mechanisms responsible for fetal programming include DNA methylation and histone modifications. Alterations in the genome can be passed through multiple generations. Maternal environment (nutrition, age, physiologic status) can program progeny heifer growth and reproductive performance.

Association of maternal and nutrient supply line factors with DNA methylation at the imprinted IGF2/H19 locus in multiple tissues of newborn twins

Epigenetic events are crucial for early development, but can be influenced by environmental factors, potentially programming the genome for later adverse health outcomes. The insulin-like growth factor 2 (IGF2)/H19 locus is crucial for prenatal growth and the epigenetic state at this locus is environmentally labile. Recent studies have implicated maternal factors, including folate intake and smoking, in the regulation of DNA methylation at this locus, although data are often conflicting in the direction and magnitude of effect. Most studies have focused on single tissues and on one or two differentially-methylated regions (DMRs) regulating IGF2/H19 expression. In this study, we investigated the relationship between multiple shared and non-shared gestational/maternal factors and DNA methylation at four IGF2/H19 DMRs in five newborn cell types from 67 pairs of monozygotic and 49 pairs of dizygotic twins. Data on maternal and non-shared supply line factors were collected during the second and third trimesters of pregnancy and DNA methylation was measured via mass spectrometry using Sequenom MassArray EpiTyper analysis. Our exploratory approach showed that the site of umbilical cord insertion into the placenta in monochorionic twins has the strongest positive association with methylation in all IGF2/H19 DMRs (p<0.05). Further, evidence for tissue- and locus-specific effects were observed, emphasizing that responsiveness to environmental exposures in utero cannot be generalized across genes and tissues, potentially accounting for the lack of consistency in previous findings. Such complexity in responsiveness to environmental exposures in utero has implications for all epigenetic studies investigating the developmental origins of health and disease.

Developmental programming of obesity and metabolic dysfunction: role of prenatal stress and stress biology

Epidemiological, clinical, physiological, cellular and molecular evidence suggests the origins of obesity and metabolic dysfunction can be traced back to intrauterine life and supports an important role for maternal nutrition prior to and during gestation in fetal programming. The elucidation of underlying mechanisms is an area of interest and intense investigation. We propose that in addition to maternal nutrition-related processes, it may be important to concurrently consider the potential role of intrauterine stress and stress biology. We frame our arguments in the larger context of an evolutionary-developmental perspective that supports roles for both nutrition and stress as key environmental conditions driving natural selection and developmental plasticity. We suggest that intrauterine stress exposure may interact with the nutritional milieu, and that stress biology may represent an underlying mechanism mediating the effects of diverse intrauterine perturbations, including but not limited to maternal nutritional insults (undernutrition and overnutrition), on brain and peripheral targets of programming of body composition, energy balance homeostasis and metabolic function. We discuss putative maternal-placental-fetal endocrine and immune/inflammatory candidate processes that may underlie the long-term effects of intrauterine stress.

Epigenetics of gestational diabetes mellitus and offspring health: the time for action is in early stages of life

The epidemic increase of type 2 diabetes and obesity in developed countries cannot be explained by overnutrition, physical inactivity and/or genetic factors alone. Epidemiologic evidence suggests that an adverse intrauterine environment, in particular a shortage or excess of nutrients is associated with increased risks for many complex diseases later in life. An impressive example for the 'fetal origins of adult disease' is gestational diabetes mellitus which usually presents in 1% to >10% of third trimester pregnancies. Intrauterine hyperglycemia is not only associated with increased perinatal morbidity and mortality, but also with increased lifelong risks of the exposed offspring for obesity, metabolic, cardiovascular and malignant diseases. Accumulating evidence suggests that fetal overnutrition (and similarly undernutrition) lead to persistent epigenetic changes in developmentally important genes, influencing neuroendocrine functions, energy homeostasis and metabolism. The concept of fetal programming has important implications for reproductive medicine. Because during early development the epigenome is much more vulnerable to environmental cues than later in life, avoiding adverse environmental factors in the periconceptional and intrauterine period may be much more important for the prevention of adult disease than any (i.e. dietetic) measures in infants and adults. A successful pregnancy should not primarily be defined by the outcome at birth but also by the health status in later life.

Critical developmental periods in the pathogenesis of hypertension

Hypertension is one of the major risk factor of cardiovascular diseases, but after a century of clinical and basic research, the discrete etiology of this disease is still not fully understood. One reason is that blood pressure is a quantitative trait with multifactorial determination. Numerous genes, environmental factors as well as epigenetic factors should be considered. There is no doubt that although the full manifestation of hypertension and other cardiovascular diseases usually occurs predominantly in adulthood and/or senescence, the roots can be traced back to early ontogeny. The detailed knowledge of the ontogenetic changes occurring in the cardiovascular system of experimental animals during particular critical periods (developmental windows) could help to solve this problem in humans and might facilitate the age-specific prevention of human hypertension. We thus believe that this approach might contribute to the reduction of cardiovascular morbidity among susceptible individuals in the future.

Maternal first-trimester diet and childhood bone mass: the Generation R Study

BACKGROUND

Maternal diet during pregnancy has been suggested to influence bone health in later life.

OBJECTIVE

We assessed the association of maternal first-trimester dietary intake during pregnancy with childhood bone mass.

DESIGN

In a prospective cohort study in 2819 mothers and their children, we measured first-trimester daily energy, protein, fat, carbohydrate, calcium, phosphorus, and magnesium intakes by using a food-frequency questionnaire and homocysteine, folate, and vitamin B-12 concentrations in venous blood. We measured childhood total body bone mass by using dual-energy X-ray absorptiometry at the median age of 6.0 y.

RESULTS

Higher first-trimester maternal protein, calcium, and phosphorus intakes and vitamin B-12 concentrations were associated with higher childhood bone mass, whereas carbohydrate intake and homocysteine concentrations were associated with lower childhood bone mass (all P-trend < 0.01). Maternal fat, magnesium intake, and folate concentrations were not associated with childhood bone mass. In the fully adjusted regression model that included all dietary factors significantly associated with childhood bone mass, maternal phosphorus intake and homocysteine concentrations most-strongly predicted childhood bone mineral content (BMC) [β = 2.8 (95% CI: 1.1, 4.5) and β = -1.8 (95% CI: -3.6, 0.1) g per SD increase, respectively], whereas maternal protein intake and vitamin B-12 concentrations most strongly predicted BMC adjusted for bone area [β = 2.1 (95% CI: 0.7, 3.5) and β = 1.8 (95% CI: 0.4, 3.2) g per SD increase, respectively].

CONCLUSION

Maternal first-trimester dietary factors are associated with childhood bone mass, suggesting that fetal nutritional exposures may permanently influence bone development.

Maternal dietary intake during pregnancy has longstanding consequences for the health of her offspring

Over the past 100 years, advances in pharmaceutical and medical technology have reduced the burden of communicable disease, and our appreciation of the mechanisms underlying the development of noncommunicable disease has broadened. During this time, a number of studies, both in humans and animal models, have highlighted the importance of maintaining an optimal diet during pregnancy. In particular, a number of studies support the hypothesis that suboptimal maternal protein and fat intake during pregnancy can have long-term effects on the growing fetus, and increase the likelihood of these offspring developing cardiovascular, renal, or metabolic diseases in adulthood. More recently, it has been shown that dietary intake of a number of micronutrients may offset or reverse the deleterious effects of macronutrient imbalance. Furthermore, maternal fat intake has also been identified as a major contributor to a healthy fetal environment, with a beneficial role for unsaturated fats during development as well as a beneficial impact on cell membrane physiology. Together these studies indicate that attempts to optimise maternal nutrition may prove to be an efficient and cost-effective strategy for preventing the development of cardiovascular, renal, or metabolic diseases.

Intrauterine calorie restriction affects placental DNA methylation and gene expression

Maternal nutrient restriction causes the development of adult onset chronic diseases in the intrauterine growth restricted (IUGR) fetus. Investigations in mice have shown that either protein or calorie restriction during pregnancy leads to glucose intolerance, increased fat mass, and hypercholesterolemia in adult male offspring. Some of these phenotypes are shown to persist in successive generations. The molecular mechanisms underlying IUGR remain unclear. The placenta is a critical organ for mediating changes in the environment and the development of embryos. To shed light on molecular mechanisms that might affect placental responses to differing environments we examined placentas from mice that had been exposed to different diets. We measured gene expression and whole genome DNA methylation in both male and female placentas of mice exposed to either caloric restriction or ad libitum diets. We observed several differentially expressed pathways associated with IUGR phenotypes and, most importantly, a significant decrease in the overall methylation between these groups as well as sex-specific effects that are more pronounced in males. In addition, a set of significantly differentially methylated genes that are enriched for known imprinted genes were identified, suggesting that imprinted loci may be particularly susceptible to diet effects. Lastly, we identified several differentially methylated microRNAs that target genes associated with immunological, metabolic, gastrointestinal, cardiovascular, and neurological chronic diseases, as well as genes responsible for transplacental nutrient transfer and fetal development.

Ecological epigenetics: an introduction to the symposium

Phenotypic variation arises from interactions between environmental and genetic variation, and the emergence of such variation is, in part, mediated by epigenetic mechanisms: factors that modify gene expression but do not change the gene sequence, per se. The role of epigenetic variation and inheritance in natural populations, however, remains poorly understood. The budding field of Ecological Epigenetics seeks to extend our knowledge of epigenetic mechanisms and processes to natural populations, and recent conceptual and technical advances have made progress toward this goal more feasible. In light of these breakthroughs, now is a particularly opportune time to develop a framework that will guide and facilitate exceptional studies in Ecological Epigenetics. Toward this goal, the Ecological Epigenetics symposium brought together researchers with diverse strengths in theory, developmental genetics, ecology, and evolution, and the proceedings from their talks are presented in this issue. By characterizing environmentally dependent epigenetic variation in natural populations, we will enhance our understanding of developmental, ecological, and evolutionary phenomena. In particular, ecological epigenetics has the potential to explain how populations endure (or fail to endure) profound and rapid environmental change. Here, my goal is to introduce some of the common goals and challenges shared by those pursuing this critical field.

Foetal life protein restriction in male mink (Neovison vison) kits lowers post-weaning protein oxidation and the relative abundance of hepatic fructose-1,6-bisphosphatase mRNA

Foetal life malnutrition has been studied intensively in a number of animal models. Results show that especially foetal life protein malnutrition can lead to metabolic changes later in life. This might be of particular importance for strict carnivores, for example, cat and mink (Neovison vison) because of their higher protein requirement than in other domestic mammals. This study aimed to investigate the effects of low protein provision during foetal life to male mink kits on their protein metabolism during the early post-weaning period of rapid growth and to investigate whether foetal life protein deficiency affects the response to adequate or deficient protein provision post weaning. Further, we intended to study whether the changes in the gene expression of key enzymes in foetal hepatic tissue caused by maternal protein deficiency were manifested post-weaning. A total of 32 male mink kits born to mothers fed either a low-protein diet (LP), that is, 14% of metabolizable energy (ME) from protein (foetal low - FL), n = 16, or an adequate-protein (AP) diet, that is, 29% of ME from protein (foetal adequate - FA), n = 16) in the last 16.3 ± 1.8 days of pregnancy were used. The FL offspring had lower birth weight and lower relative abundance of fructose-1,6-bisphosphatase (Fru-1,6-P2ase) and pyruvate kinase mRNA in foetal hepatic tissue than FA kits. The mothers were fed a diet containing adequate protein until weaning. At weaning (7 weeks of age), half of the kits from each foetal treatment group were fed an AP diet (32% of ME from protein; n = 8 FA and 8 FL) and the other half were fed a LP diet (18% of ME from protein; n = 8 FA and 8 FL) until 9.5 weeks of age, yielding four treatment groups (i.e. FA-AP, FA-LP, FL-AP and FL-LP). Low protein provision in foetal life lowered the protein oxidation post-weaning compared with the controls (P = 0.006), indicating metabolic flexibility and a better ability to conserve protein. This could not, however, be supported by changes in liver mass because of foetal life experience. A lower relative abundance of Fru-1,6-P2ase mRNA was observed (P < 0.05), being lower in 9.5-week-old FL than in FA kits. It can be concluded that foetal life protein restriction leads to changes in post-weaning protein metabolism through lower protein oxidation of male mink kits.

The role of methylation of DNA in environmental adaptation

Methylation of DNA is an epigenetic mechanism that influences patterns of gene expression. DNA methylation marks contribute to adaptive phenotypic variation but are erased during development. The role of DNA methylation in adaptive evolution is therefore unclear. We propose that environmentally-induced DNA methylation causes phenotypic heterogeneity that provides a substrate for selection via forces that act on the epigenetic machinery. For example, selection can alter environmentally-induced methylation of DNA by acting on the molecular mechanisms used for the genomic targeting of DNA methylation. Another possibility is that specific methylation marks that are environmentally-induced, yet non-heritable, could influence preferential survival and lead to consistent methylation of the same genomic regions over time. As methylation of DNA is known to increase the likelihood of cytosine-to-thymine transitions, non-heritable adaptive methylation marks can drive an increased likelihood of mutations targeted to regions that are consistently marked across several generations. Some of these mutations could capture, genetically, the phenotypic advantage of the epigenetic mark. Thereby, selectively favored transitory alterations in the genome invoked by DNA methylation could ultimately become selectable genetic variation through mutation. We provide evidence for these concepts using examples from different taxa, but focus on experimental data on large-scale DNA sequencing that expose between-group genetic variation after bidirectional selection on honeybees, Apis mellifera.