Epigenetic changes in fetal hypothalamic energy regulating pathways are associated with maternal undernutrition and twinning

Developmental programming of hypothalamic neuronal circuits: impact on energy balance control

The prevalence of obesity in adults and children has increased globally at an alarming rate. Mounting evidence from both epidemiological studies and animal models indicates that adult obesity and associated metabolic disorders can be programmed by intrauterine and early postnatal environment- a phenomenon known as "fetal programming of adult disease." Data from nutritional intervention studies in animals including maternal under- and over-nutrition support the developmental origins of obesity and metabolic syndrome. The hypothalamic neuronal circuits located in the arcuate nucleus controlling appetite and energy expenditure are set early in life and are perturbed by maternal nutritional insults. In this review, we focus on the effects of maternal nutrition in programming permanent changes in these hypothalamic circuits, with experimental evidence from animal models of maternal under- and over-nutrition. We discuss the epigenetic modifications which regulate hypothalamic gene expression as potential molecular mechanisms linking maternal diet during pregnancy to the offspring's risk of obesity at a later age. Understanding these mechanisms in key metabolic genes may provide insights into the development of preventative intervention strategies.

Duration of maternal undernutrition differentially alters fetal growth and hormone concentrations

To investigate the impact of duration of maternal undernutrition in twin sheep pregnancies, ewes were either fed 100% (C) or 50% of their nutrient requirements from 28 to 78 d gestational age (dGA) and readjusted to 100% beginning at 79 dGA (LC) or continuously restricted from 28 to 135 dGA (LL). Weights of the fetus, empty carcass, brain, and liver were greater in the LC than LL fetuses at 135 dGA (P ≤ 0.05). Although umbilical vein (UmV) glucose concentrations did not differ, the UmV:umbilical artery (UmA) glucose gradient was smaller (0.26 ± 0.03 vs 0.38 ± 0.03 and 0.39 ± 0.04 mmol L(-1); P ≤ 0.05) in LL than C and LC fetuses, respectively. Umbilical vein concentrations of IGF-1 were less (46.7 ± 5.62 vs 74.3 ± 6.71 ng/mL; P ≤ 0.05) in LL than LC fetuses. Additionally, LL fetuses tended (P ≤ 0.10) to have lower UmA concentrations of insulin (0.24 ± 0.13 vs 0.70 ± 0.15 ng/mL) and IGF-1 (66.6 ± 7.51 vs 91.4 ± 8.97 ng/mL) than LC fetuses. Although most of the observed differences occurred between LC and LL pregnancies, LC fetuses tended (P ≤ 0.10) to have greater UmV and UmA pCO2 than C fetuses. Furthermore, the UmV:UmA O2 content gradient tended to be greater (5.02 ± 0.43 vs 3.41 ± 0.47; P ≤ 0.10) in C than LL fetuses. UmA placental lactogen also tended to be greater (46.6 ± 4.40 vs 31.1 ± 4.69 ng/mL; P ≤ 0.10) in LL than C fetuses. These data suggest that in twin pregnancies, maternal undernutrition followed by realimentation induces a different fetal outcome compared with continuous nutrient restriction, and both may differ physiologically from control fed pregnancies.

Telomere length in the two extremes of abnormal fetal growth and the programming effect of maternal arterial hypertension

We tested the hypothesis that leukocyte telomere length (LTL) is associated with birth weight in both extremes of abnormal fetal growth: small (SGA) and large for gestational age newborns (LGA). Clinical and laboratory variables of the mothers and the neonates were explored; 45 newborns with appropriate weight for gestational age (AGA), 12 SGA and 12 LGA were included. Whether the differences might be explained by variation in OBFC1 (rs9419958) and CTC1 (rs3027234) genes associated with LTL was determined. A significant association between birth weight and LTL was observed; LTL was significantly shorter in LGA newborns (1.01 ± 0.12) compared with SGA (1.73 ± 0.19) p < 0.005, mean ± SE. Maternal (Spearman R = −0.6, p = 0.03) and neonatal LTL (R = −0.25, p = 0.03) were significantly and inversely correlated with maternal history of arterial hypertension in previous gestations. Neonatal LTL was not significantly associated with either rs9419950 or rs3027234, suggesting that the association between neonatal LTL and birth weight is not influenced by genetic variation in genes that modify the interindividual LTL. In conclusion, telomere biology seems to be modulated by abnormal fetal growth; modifications in telomere length might be programmed by an adverse environment in utero.

Feeding behaviour in ruminants: a consequence of interactions between a reward system and the regulation of metabolic homeostasis

Feeding behaviour, through both diet selection and food intake, is the predominant way that an animal attempts to fulfil its metabolic requirements and achieve homeostasis. In domestic herbivores across the wide range of production practices, voluntary feed intake is arguably the most important factor in animal production, and a better understanding of systems involved in intake regulation can have important practical implications in terms of performance, health and welfare. In this review, we provide a conceptual framework that highlights the critical involvement and interconnections of two major regulatory systems of feeding behaviour: the reward and the homeostatic systems. A review of the literature on ruminants and rodents provides evidence that feeding behaviour is not only shaped by homeostatic needs but also by hedonic and motivational incentives associated with foods through experiences and expectations of rewards. The different brain structures and neuronal/hormonal pathways involved in these two regulatory systems is evidence of their different influences on feeding behaviours that help explain deviation from behaviour based solely on satisfying nutritional needs, and offers opportunities to influence feeding motivation to meet applied goals in livestock production. This review further highlights the key contribution of experience in the short (behavioural learning) and long term (metabolic learning), including the critical role of fetal environment in shaping feeding behaviour both directly by food cue–consequence pairings and indirectly via modifications of metabolic functioning, with cascading effects on energy balance and body reserves and, consequently, on feeding motivation.

Insights from space: potential role of diet in the spatial organization of chromosomes

We can now sequence and identify genome wide epigenetic patterns and perform a variety of "genomic experiments" within relatively short periods of time-ranging from days to weeks. Yet, despite these technological advances, we have a poor understanding of the inter-relationships between epigenetics, genome structure-function, and nutrition. Perhaps this limitation lies, in part, in our propensity to study epigenetics in terms of the linear arrangement of elements and genes. Here we propose that a more complete understanding of how nutrition impacts on epigenetics and cellular development resides within the inter-relationships between DNA and histone modification patterns and genome function, in the context of spatial organization of chromatin and the epigenome.

AZA-deoxycytidine stimulates proopiomelanocortin gene expression and ACTH secretion in human pituitary ACTH-secreting tumors

PURPOSE

It is well known that methylation plays an important role in regulating tissue expression of proopiomelanocortin (POMC) and recent studies have shown that demethylation can occur also in vitro in neuroendocrine tumors. Aim of the present study was to evaluate whether inhibition of methylation modulates POMC expression and ACTH secretion by human corticotrope tumors.

METHODS

Twenty two ACTH-secreting pituitary tumors were incubated with 5-AZA-2'-deoxycytidine (AZA), an inhibitor of DNA-methyltransferases, with or without 10 nM corticotropin-releasing hormone (CRH). Both dose response (100 nM-10 μM AZA) and time course (4-96 h) experiments were carried out for measurement of ACTH secretion and POMC gene expression.

RESULTS

Incubation with AZA increased constitutive POMC expression and ACTH secretion by human corticotrope adenomas. The effect appeared most notable at 24 and 48 h with 1 μM AZA. Incubation with AZA did not exert an additional stimulatory effect on CRH-stimulated POMC and ACTH.

CONCLUSIONS

The present study shows that AZA increases POMC gene expression and ACTH secretion in human pituitary ACTH-secreting tumors. This can be taken to indicate that mechanisms set into motion by AZA play a role in the regulation of ACTH secretion/POMC expression in tumoral corticotropes and paves the way to further studies in Cushing's disease.

Parental diet, pregnancy outcomes and offspring health: metabolic determinants in developing oocytes and embryos

The periconceptional period, embracing the terminal stages of oocyte growth and post-fertilisation development up to implantation, is sensitive to parental nutrition. Deficiencies or excesses in a range of macro- and micronutrients during this period can lead to impairments in fertility, fetal development and long-term offspring health. Obesity and genotype-related differences in regional adiposity are associated with impaired liver function and insulin resistance, and contribute to fatty acid-mediated impairments in sperm viability and oocyte and embryo quality, all of which are associated with endoplasmic reticulum stress and compromised fertility. Disturbances to maternal protein metabolism can elevate ammonium concentrations in reproductive tissues and disturb embryo and fetal development. Associated with this are disturbances to one-carbon metabolism, which can lead to epigenetic modifications to DNA and associated proteins in offspring that are both insulin resistant and hypertensive. Many enzymes involved in epigenetic gene regulation use metabolic cosubstrates (e.g. acetyl CoA and S-adenosyl methionine) to modify DNA and associated proteins, and so act as 'metabolic sensors' providing a link between parental nutritional status and gene regulation. Separate to their genomic contribution, spermatozoa can also influence embryo development via direct interactions with the egg and by seminal plasma components that act on oviductal and uterine tissues.

Periconceptional undernutrition in sheep leads to decreased locomotor activity in a natural environment

Maternal undernutrition during pregnancy increases offspring obesity and metabolic disease risk. We hypothesized that periconceptional undernutrition in sheep from 60 days before conception through to day 30 of gestation (UN) would decrease voluntary locomotor activity in adult offspring. Distance travelled was measured at 18 months of age for ∼48 h in the paddock. Data were analysed using multiple regression analysis, with explanatory variables including sex, nutrition group, birth weight, average time between GPS measurements and percentage of time during the measurement period spent in daylight. Mean (±s.e.) distance walked (m/h) was greater for control (CON) than UN animals, and greater for females than males [110.2 (6.5), CON females; 110.7 (6.3), CON males; 105.1 (5.3), UN females and 95.5 (5.8), UN males; P = 0.02 for nutrition group effect and for sex effect]. Periconceptional undernutrition may lead to a significant decrease in voluntary physical activity in adult offspring.

MicroRNAs with Specific Roles in Diabetes and Psychiatric Diseases

Diabetes mellitus is one of the most cited non communicable diseases and the most common metabolic disorder. Epigenetics represents the field of study of heritable changes in gene expression which are not directly related to DNA. Epigenetics is concerned, alongside histone modifications, short interfering RNAs etc., with microRNAs (miRNAs) as well. These are small noncoding RNAs, 21 to 23 nucleotides in length, which either inhibit translation or affect mRNA stability and degradation. At present, there are dozens of miRNAs which have been proven to be involved in the animal and human pathology of diabetes (type 1 or 2). This review focuses on the miRNAs which have been identified as playing a role in both psychiatric diseases and diabetes.

Eating behavior and stress: a pathway to obesity

Stress causes or contributes to a huge variety of diseases and disorders. Recent evidence suggests obesity and other eating-related disorders may be among these. Immediately after a stressful event is experienced, there is a corticotropin-releasing-hormone (CRH)-mediated suppression of food intake. This diverts the body’s resources away from the less pressing need to find and consume food, prioritizing fight, flight, or withdrawal behaviors so the stressful event can be dealt with. In the hours following this, however, there is a glucocorticoid-mediated stimulation of hunger and eating behavior. In the case of an acute stress that requires a physical response, such as a predator-prey interaction, this hypothalamic-pituitary-adrenal (HPA) axis modulation of food intake allows the stressful event to be dealt with and the energy used to be replaced afterward. In the case of ongoing psychological stress, however, chronically elevated glucocorticoids can lead to chronically stimulated eating behavior and excessive weight gain. In particular, stress can enhance the propensity to eat high calorie “palatable” food via its interaction with central reward pathways. Activation of this circuitry can also interact with the HPA axis to suppress its further activation, meaning not only can stress encourage eating behavior, but eating can suppress the HPA axis and the feeling of stress. In this review we will explore the theme of eating behavior and stress and how these can modulate one another. We will address the interactions between the HPA axis and eating, introducing a potential integrative role for the orexigenic hormone, ghrelin. We will also examine early life and epigenetic modulation of the HPA axis and how this can influence eating behavior. Finally, we will investigate the clinical implications of changes to HPA axis function and how this may be contributing to obesity in our society.

Excess body weight during pregnancy and offspring obesity: potential mechanisms

The rates of child and adult obesity have increased in most developed countries over the past several decades. The health consequences of obesity affect both physical and mental health, and the excess body weight can be linked to an elevated risk for developing type 2 diabetes, cardiovascular problems, and depression. Among the factors that can influence the development of obesity are higher infant weights and increased weight gain, which are associated with higher risk for excess body weight later in life. In turn, mother's excess body weight during and after pregnancy can be linked to the risk for offspring overweight and obesity through dietary habits, mode of delivery and feeding, breast milk composition, and through the influence on infant gut microbiota. This review considers current knowledge of these potential mechanisms that threaten to create an intergenerational cycle of obesity.

Hypothalamic and brainstem neuronal circuits controlling homeostatic energy balance

Alterations in adequate energy balance maintenance result in serious metabolic disturbances such as obesity. In mammals, this complex process is orchestrated by multiple and distributed neuronal circuits. Hypothalamic and brainstem neuronal circuits are critically involved in the sensing of circulating and local factors conveying information about the energy status of the organism. The integration of these signals culminates in the generation of specific and coordinated physiological responses aimed at regulating energy balance through the modulation of appetite and energy expenditure. In this article, we review current knowledge on the homeostatic regulation of energy balance, emphasizing recent advances in mouse genetics, electrophysiology, and optogenetic techniques that have greatly contributed to improving our understanding of this central process.

Nutrition, epigenetics, and diseases

Increasing epidemiological evidence suggests that maternal nutrition and environmental exposure early in development play an important role in susceptibility to disease in later life. In addition, these disease outcomes seem to pass through subsequent generations. Epigenetic modifications provide a potential link between the nutrition status during critical periods in development and changes in gene expression that may lead to disease phenotypes. An increasing body of evidence from experimental animal studies supports the role of epigenetics in disease susceptibility during critical developmental periods, including periconceptional period, gestation, and early postnatal period. The rapid improvements in genetic and epigenetic technologies will allow comprehensive investigations of the relevance of these epigenetic phenomena in human diseases.

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

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

Can proopiomelanocortin methylation be used as an early predictor of metabolic syndrome?

OBJECTIVE

The objectives of this study were to compare early predictive marker of the metabolic syndrome with proopiomelanocortin (POMC) methylation status and to determine the association among birth weight, ponderal index, and cord blood methylation status.

RESEARCH DESIGN AND METHODS

We collected pregnancy outcome data from pregnant women, cord blood samples at delivery, and blood from children (7-9 years old; n = 90) through a prospective cohort study at Ewha Womans University, MokDong Hospital (Seoul, Korea), from 2003-2005. POMC methylation was assessed by pyrosequencing. We divided subjects into three groups according to cord blood POMC methylation: the low methylation (<10th percentile), mid-methylation, and high methylation (>90th percentile) groups. We analyzed the association of POMC methylation status at birth with adiposity and metabolic components using ANCOVA and multiple linear regression analysis.

RESULTS

Birth weights (P = 0.01) and ponderal indices (P = 0.01) in the high POMC methylation group were significantly lower than in the mid-POMC methylation group. In terms of metabolic components of childhood, blood triglycerides (57.97, 67.29 vs. 113.89 mg/dL; P = 0.03, 0.01) and insulin (7.10, 7.64 vs. 10.13 μIU/mL; P = 0.05, 0.02) at childhood were significantly higher in the high POMC methylation group than in the low and mid-POMC methylation group.

CONCLUSIONS

High POMC methylation in cord blood was associated with lower birth weight, and children with high POMC methylation in cord blood showed higher triglycerides and higher insulin concentrations in blood. Thus, POMC methylation status in cord blood may be an early predictive marker of future metabolic syndrome.

Role of prenatal undernutrition in the expression of serotonin, dopamine and leptin receptors in adult mice: implications of food intake

Perturbations in the levels of serotonin expression have a significant impact on behavior and have been implicated in the pathogenesis of several neuropsychiatric disorders including anxiety, mood and appetite. Fetal programming is a risk factor for the development of metabolic diseases during adulthood. Moreover, previous studies have shown that serotonin (5-HT), dopamine and leptin are important in energy balance. In the present study, the impact of maternal malnutrition-induced prenatal undernutrition (UN) was investigated in mice and the expression of 5-HT_1A, dopamine (D)1, D2 and Ob-Rb receptors was analyzed in the hypothalamus during adulthood. The UN group showed a low birth weight compared with the control group. With regard to receptor expression, 5-HT_1A in the UN group was increased in the hypothalamus and D1 was reduced, whereas D2 showed an increase from postnatal day (P)14 in the arcuate nucleus. Ob-Rb receptor expression was increased in the hypothalamus at P14 and P90. These observations indicated that maternal caloric restriction programs a postnatal body weight gain in offspring with an increased food intake in early postnatal life which continues into adulthood. In addition, UN in mice was found to be affected by Ob-Rb, 5-HT_1A and D1/2 receptor expression, indicating that these observations may be associated with hyperphagia and obesity.

Epigenetic programming of reward function in offspring: a role for maternal diet

Early life development, through gestation and lactation, represents a timeframe of extreme vulnerability for the developing fetus in general, and for the central nervous system in particular. An adverse perinatal environment can have a lasting negative impact on brain development, increasing the risk for developmental disorders and broader psychopathologies. A major determinant of the fetal developmental environment is maternal diet. The present review summarizes the current literature regarding the effect of poor maternal perinatal nutrition on offspring brain development, with an emphasis on reward-related neural systems and behaviors. Epigenetic mechanisms represent a likely link between maternal diet and persistent changes in offspring brain development, and these mechanisms are presented and discussed within the context of perinatal maternal nutrition.

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.

Feed your head: neurodevelopmental control of feeding and metabolism

During critical periods of development early in life, excessive or scarce nutritional environments can disrupt the development of central feeding and metabolic neural circuitry, leading to obesity and metabolic disorders in adulthood. A better understanding of the genetic networks that control the development of feeding and metabolic neural circuits, along with knowledge of how and where dietary signals disrupt this process, can serve as the basis for future therapies aimed at reversing the public health crisis that is now building as a result of the global obesity epidemic. This review of animal and human studies highlights recent insights into the molecular mechanisms that regulate the development of central feeding circuitries, the mechanisms by which gestational and early postnatal nutritional status affects this process, and approaches aimed at counteracting the deleterious effects of early over- and underfeeding.

Major epigenetic development distinguishing neuronal and non-neuronal cells occurs postnatally in the murine hypothalamus

Prenatal and early postnatal environment can persistently alter one's risk of obesity. Environmental effects on hypothalamic developmental epigenetics constitute a likely mechanism underlying such 'developmental programming' of energy balance regulation. To advance our understanding of these processes, it is essential to develop approaches to disentangle the cellular and regional heterogeneity of hypothalamic developmental epigenetics. We therefore performed genome-scale DNA methylation profiling in hypothalamic neurons and non-neuronal cells at postnatal day 0 (P0) and P21 and found, surprisingly, that most of the DNA methylation differences distinguishing these two cell types are established postnatally. In particular, neuron-specific increases in DNA methylation occurred extensively at genes involved in neuronal development. Quantitative bisulfite pyrosequencing verified our methylation profiling results in all 15 regions examined, and expression differences were associated with DNA methylation at several genes. We also identified extensive methylation differences between the arcuate (ARH) and paraventricular nucleus of the hypothalamus (PVH). Integrating these two data sets showed that genomic regions with PVH versus ARH differential methylation strongly overlap with those undergoing neuron-specific increases from P0 to P21, suggesting that these developmental changes occur preferentially in either the ARH or PVH. In particular, neuron-specific methylation increases at the 3' end of Shh localized to the ARH and were positively associated with gene expression. Our data indicate a key role for DNA methylation in establishing the gene expression potential of diverse hypothalamic cell types, and provide the novel insight that early postnatal life is a critical period for cell type-specific epigenetic development in the murine hypothalamus.

Green tea extract increases mRNA expression of enzymes which influence epigenetic marks in newborn female offspring from undernourished pregnant mother

Biochemical and toxicological properties of catechin remain unclear, e.g.; how catechin affects female offspring from undernourished pregnant dams. Here, to elucidate effects of low prenatal protein on female offspring health status, changes of enzymes which modify epigenetic marks related with metabolism in kidneys from newborns were investigated after continuously administering catechin extracted from green tea to lactating maternal rats after pregnant undernourishment. We found that green tea extract intake during lactation up-regulated the activation of AMP-activated protein kinase in young female offspring from protein-restricted dams and modulated the AMP-activated protein kinase pathway in the kidney. This pathway was indicated to be stimulated by SIRT1 gene expression. The feeding of green tea extract to protein-restricted dams during lactation is likely to up-regulate AMP-activated protein kinase activation and may partly lead to alterations of the AMP-activated protein kinase pathway in female offspring kidneys. In addition, energy metabolism in fetal and offspring period with green tea extract administration might be related to enzymes which modify epigenetic marks such as DNA methyltransferase 1 and 3a.

Perinatal nutrition programs neuroimmune function long-term: mechanisms and implications

Our early life nutritional environment can influence several aspects of physiology, including our propensity to become obese. There is now evidence to suggest perinatal diet can also independently influence development of our innate immune system. This review will address three not-necessarily-exclusive mechanisms by which perinatal nutrition can program neuroimmune function long-term: by predisposing the individual to obesity, by altering the gut microbiota, and by inducing epigenetic modifications that alter gene transcription throughout life.

Common phenotypes and the developmental origins of disease

PURPOSE OF REVIEW

The association between nutrition during pregnancy and the development of metabolic disease in the offspring has been well evidenced in humans and animals. Whilst evidence has accumulated to support various theories linking maternal diet to long-term health, the precise mechanisms of action remain poorly understood. This review summarizes recent advances within the field, focusing on the use of animal models to investigate common phenotypic outcomes.

RECENT FINDINGS

Continued characterization of postnatal phenotypes has highlighted the importance of postnatal diet in unmasking programming effects of prenatal diet. Whilst common phenotypes are observed across models, differences in associated regulatory processes exist dependent upon the dietary exposure used and sex of the offspring. The use of unbiased techniques at developmental stages has identified gene pathways sensitive to maternal diet, potentially explaining the induction of a common phenotype by different nutritional interventions. Evidence has also grown to support the role of epigenetic modification, with an increasing range of targets identified as being sensitive.

SUMMARY

A challenge remains in identifying the direct functional and long-term consequences of changes in gene expression or epigenetic status during development, and to translate these back to human populations.

Perinatal programming of neuroendocrine mechanisms connecting feeding behavior and stress

Feeding behavior is closely regulated by neuroendocrine mechanisms that can be influenced by stressful life events. However, the feeding response to stress varies among individuals with some increasing and others decreasing food intake after stress. In addition to the impact of acute lifestyle and genetic backgrounds, the early life environment can have a life-long influence on neuroendocrine mechanisms connecting stress to feeding behavior and may partially explain these opposing feeding responses to stress. In this review I will discuss the perinatal programming of adult hypothalamic stress and feeding circuitry. Specifically I will address how early life (prenatal and postnatal) nutrition, early life stress, and the early life hormonal profile can program the hypothalamic-pituitary-adrenal (HPA) axis, the endocrine arm of the body's response to stress long-term and how these changes can, in turn, influence the hypothalamic circuitry responsible for regulating feeding behavior. Thus, over- or under-feeding and/or stressful events during critical windows of early development can alter glucocorticoid (GC) regulation of the HPA axis, leading to changes in the GC influence on energy storage and changes in GC negative feedback on HPA axis-derived satiety signals such as corticotropin-releasing-hormone. Furthermore, peripheral hormones controlling satiety, such as leptin and insulin are altered by early life events, and can be influenced, in early life and adulthood, by stress. Importantly, these neuroendocrine signals act as trophic factors during development to stimulate connectivity throughout the hypothalamus. The interplay between these neuroendocrine signals, the perinatal environment, and activation of the stress circuitry in adulthood thus strongly influences feeding behavior and may explain why individuals have unique feeding responses to similar stressors.

Fetal metabolic programming and epigenetic modifications: a systems biology approach

A growing body of evidence supports the notion that epigenetic changes such as DNA methylation and histone modifications, both involving chromatin remodeling, contribute to fetal metabolic programming. We use a combination of gene-protein enrichment analysis resources along with functional annotations and protein interaction networks for an integrative approach to understanding the mechanisms underlying fetal metabolic programming. Systems biology approaches suggested that fetal adaptation to an impaired nutritional environment presumes profound changes in gene expression that involve regulation of tissue-specific patterns of methylated cytosine residues, modulation of the histone acetylation-deacetylation switch, cell differentiation, and stem cell pluripotency. The hypothalamus and the liver seem to be differently involved. In addition, new putative explanations have emerged about the question of whether in utero overnutrition modulates fetal metabolic programming in the same fashion as that of a maternal environment of undernutrition, suggesting that the mechanisms behind these two fetal nutritional imbalances are different. In conclusion, intrauterine growth restriction is most likely to be associated with the induction of persistent changes in tissue structure and functionality. Conversely, a maternal obesogenic environment is most probably associated with metabolic reprogramming of glucose and lipid metabolism, as well as future risk of metabolic syndrome (MS), fatty liver, and insulin (INS) resistance.

Development of the hypothalamic melanocortin system

The melanocortin system is a critical component of the forebrain and hindbrain regulatory systems involved in energy balance. This system is composed of pro-opiomelanocortin (POMC) neurons that act, in part, through the melanocortin-4 receptor (MC4R). Although the importance of the melanocortin system in controlling feeding has been established for two decades, the understanding of the developmental substrates underlying POMC and MC4R neuron development and function has just begun to emerge. The formation of the melanocortin system involves several discrete developmental steps that include the birth and fate specification of POMC- and MC4R-containing neurons and the extension and guidance of POMC axons to their MC4R-expressing target nuclei. Each of these developmental processes appears to require specific sets of genes and developmental cues that include perinatal hormones. Recent evidence has also highlighted the importance of perinatal nutrition in controlling the ultimate architecture of the melanocortin system.

The secret language of destiny: stress imprinting and transgenerational origins of disease

Epigenetic regulation modulates gene expression without altering the DNA sequence to facilitate rapid adjustments to dynamically changing environmental conditions. The formation of an epigenetic memory allows passing on this information to subsequent generations. Here we propose that epigenetic memories formed by adverse environmental conditions and stress represent a critical determinant of health and disease in the F3 generation and beyond. Transgenerational programming of epigenetic regulation may represent a key to understand adult-onset complex disease pathogenesis and cumulative effects of life span and familial disease etiology. Ultimately, the mechanisms of generating an epigenetic memory may become of potentially promising diagnostic and therapeutic relevance due to their reversible nature. Exploring the role of environmental factors, such as stress, in causing variations in epigenetic profiles may lead to new avenues of personalized, preventive medicine based on epigenetic signatures and interventions.

Molecular mechanisms underlying the fetal programming of adult disease

Adverse events in utero can be critical in determining quality of life and overall health. It is estimated that up to 50 % of metabolic syndrome diseases can be linked to an adverse fetal environment. However, the mechanisms linking impaired fetal development to these adult diseases remain elusive. This review uncovers some of the molecular mechanisms underlying how normal physiology may be impaired in fetal and postnatal life due to maternal insults in pregnancy. By understanding the mechanisms, which include epigenetic, transcriptional, endoplasmic reticulum (ER) stress, and reactive oxygen species (ROS), we also highlight how intervention in fetal and neonatal life may be able to prevent these diseases long-term.

Size at birth and adult fat mass in twin sheep are determined in early gestation

Size at birth is related to adult health outcomes. Twins are born smaller than singletons; this has been assumed to be secondary to limited nutrient supply in late gestation.We hypothesised that growth trajectory in twins, and the adult consequences of being conceived a twin, are determined in early gestation. Twin pregnancies in sheep were randomised to reduction of one twin on day 42 of a 148 day pregnancy by intra-thoracic KCl (Reductions, n =46) or a sham procedure (Twins, n =22). Singleton-bearing ewes also underwent a sham procedure (n =27). Ewes lambed spontaneously. Linear measures of size at birth were similar in Twins and Reductions, and significantly less than in Singletons. Birthweight was lower in Twins and Reductions than in Singletons, and less in Twins than in Reductions (means (SEM): Singletons, liveborn n =23: 6.59 (0.17) kg; Twins, liveborn n =36: 5.23 (0.16) kg; Reductions, liveborn n =27: 5.76 (0.15) kg; all comparisons P <0.05). Reductions grew most rapidly between birth and weaning (Singletons, 20.0 (0.4) g kg⁻¹ day⁻¹; Twins, 20.0 (0.3) g kg⁻¹ day⁻¹; Reductions, 21.0 (0.3) g kg⁻¹ day⁻¹, P <0.05) and were of similar weight as Singletons by weaning; Twins remained smaller by weaning but grew most rapidly thereafter (Singletons, 1.6 (0.1) g kg⁻¹ day⁻¹; Twins, 2.1 (0.1) g kg⁻¹ day⁻¹; Reductions, 1.6 (0.1) g kg⁻¹ day⁻¹, P <0.01), so that all groups had similar weight at 2 years. However, Twins and Reductions had greater percentage fat mass than Singletons at 2 years (Singletons, 11.1 (1.1)%; Twins, 14.8 (1.2)%; Reductions, 15.5 (1.1)%, P <0.05). Thus, in twins, fetal growth trajectory, linear size at birth and adult fat mass are largely determined in early gestation. If this is also true in humans, there are important implications for interventions aimed at optimising fetal growth and pregnancy outcome.