Genetic and epigenetic variation of the glucocorticoid receptor (NR3C1) in placenta and infant neurobehavior

Epigenetics across the human lifespan

Epigenetics has the potential to explain various biological phenomena that have heretofore defied complete explication. This review describes the various types of endogenous human developmental milestones such as birth, puberty, and menopause, as well as the diverse exogenous environmental factors that influence human health, in a chronological epigenetic context. We describe the entire course of human life from periconception to death and chronologically note all of the potential internal timepoints and external factors that influence the human epigenome. Ultimately, the environment presents these various factors to the individual that influence the epigenome, and the unique epigenetic and genetic profile of each individual also modulates the specific response to these factors. During the course of human life, we are exposed to an environment that abounds with a potent and dynamic milieu capable of triggering chemical changes that activate or silence genes. There is constant interaction between the external and internal environments that is required for normal development and health maintenance as well as for influencing disease load and resistance. For example, exposure to pharmaceutical and toxic chemicals, diet, stress, exercise, and other environmental factors are capable of eliciting positive or negative epigenetic modifications with lasting effects on development, metabolism and health. These can impact the body so profoundly as to permanently alter the epigenetic profile of an individual. We also present a comprehensive new hypothesis of how these diverse environmental factors cause both direct and indirect epigenetic changes and how this knowledge can ultimately be used to improve personalized medicine.

Assessment and evaluation of the high risk neonate: the NICU Network Neurobehavioral Scale

There has been a long-standing interest in the assessment of the neurobehavioral integrity of the newborn infant. The NICU Network Neurobehavioral Scale (NNNS) was developed as an assessment for the at-risk infant. These are infants who are at increased risk for poor developmental outcome because of insults during prenatal development, such as substance exposure or prematurity or factors such as poverty, poor nutrition or lack of prenatal care that can have adverse effects on the intrauterine environment and affect the developing fetus. The NNNS assesses the full range of infant neurobehavioral performance including neurological integrity, behavioral functioning, and signs of stress/abstinence. The NNNS is a noninvasive neonatal assessment tool with demonstrated validity as a predictor, not only of medical outcomes such as cerebral palsy diagnosis, neurological abnormalities, and diseases with risks to the brain, but also of developmental outcomes such as mental and motor functioning, behavior problems, school readiness, and IQ. The NNNS can identify infants at high risk for abnormal developmental outcome and is an important clinical tool that enables medical researchers and health practitioners to identify these infants and develop intervention programs to optimize the development of these infants as early as possible. The video shows the NNNS procedures, shows examples of normal and abnormal performance and the various clinical populations in which the exam can be used.

Placental FKBP5 genetic and epigenetic variation is associated with infant neurobehavioral outcomes in the RICHS cohort

Adverse maternal environments can lead to increased fetal exposure to maternal cortisol, which can cause infant neurobehavioral deficits. The placenta regulates fetal cortisol exposure and response, and placental DNA methylation can influence this function. FK506 binding protein (FKBP5) is a negative regulator of cortisol response, FKBP5 methylation has been linked to brain morphology and mental disorder risk, and genetic variation of FKBP5 was associated with post-traumatic stress disorder in adults. We hypothesized that placental FKBP5 methylation and genetic variation contribute to gene expression control, and are associated with infant neurodevelopmental outcomes assessed using the Neonatal Intensive Care Unit (NICU) Network Neurobehavioral Scales (NNNS). In 509 infants enrolled in the Rhode Island Child Health Study, placental FKBP5 methylation was measured at intron 7 using quantitative bisulfite pyrosequencing. Placental FKBP5 mRNA was measured in a subset of 61 infants by quantitative PCR, and the SNP rs1360780 was genotyped using a quantitative allelic discrimination assay. Relationships between methylation, expression and NNNS scores were examined using linear models adjusted for confounding variables, then logistic models were created to determine the influence of methylation on membership in high risk groups of infants. FKBP5 methylation was negatively associated with expression (P = 0.08, r = -0.22); infants with the TT genotype had higher expression than individuals with CC and CT genotypes (P = 0.06), and those with CC genotype displayed a negative relationship between methylation and expression (P = 0.06, r = -0.43). Infants in the highest quartile of FKBP5 methylation had increased risk of NNNS high arousal compared to infants in the lowest quartile (OR 2.22, CI 1.07-4.61). TT genotype infants had increased odds of high NNNS stress abstinence (OR 1.98, CI 0.92-4.26). Placental FKBP5 methylation reduces expression in a genotype specific fashion, and genetic variation supersedes this effect. These genetic and epigenetic differences in expression may alter the placenta's ability to modulate cortisol response and exposure, leading to altered neurobehavioral outcomes.

Postnatal epigenetic modification of glucocorticoid receptor gene in preterm infants: a prospective cohort study

OBJECTIVE

To examine the environmental effects on cytosine methylation of preterm infant's DNA, because early life experiences are considered to influence the physiological and mental health of an individual through epigenetic modification of DNA.

DESIGN

A prospective cohort study, comparison of epigenetic differences in the glucocorticoid receptor (GR) gene between healthy term and preterm infants.

SETTING

Neonatal Intensive Care Unit in a Japanese University Hospital.

PARTICIPANTS

A cohort of 40 (20 term and 20 preterm) infants was recruited on the day of birth, and peripheral blood was obtained from each infant at birth and on postnatal day 4.

MAIN OUTCOME MEASURES

The methylation rates in the 1-F promoter region of the GR gene using the Mquant method.

RESULTS

The methylation rate increased significantly between postnatal days 0 and 4 in preterm infants but remained stable in term infants. Thus, the methylation rate was significantly higher in preterm than in term infants at postnatal day 4. Several perinatal parameters were significantly correlated with this change in the methylation rate. Logistic regression analysis revealed that methylation rates at postnatal day 4 predicted the occurrence of later complications that required glucocorticoid administration during the neonatal period. No gene polymorphism was detected within the GR promoter region analysed.

CONCLUSIONS

Although further large-scale studies are needed to detect the environmental factors that explain the difference in epigenetic modification among infants after birth, our data show that the postnatal environment influences epigenetic programming of GR expression through methylation of the GR gene promoter in premature infants, which may result in relative glucocorticoid insufficiency during the postnatal period.

Relationships between lead biomarkers and diurnal salivary cortisol indices in pregnant women from Mexico City: a cross-sectional study

BACKGROUND

Lead (Pb) exposure during pregnancy may increase the risk of adverse maternal, infant, or childhood health outcomes by interfering with hypothalamic-pituitary-adrenal-axis function. We examined relationships between maternal blood or bone Pb concentrations and features of diurnal cortisol profiles in 936 pregnant women from Mexico City.

METHODS

From 2007-11 we recruited women from hospitals/clinics affiliated with the Mexican Social Security System. Pb was measured in blood (BPb) during the second trimester and in mothers' tibia and patella 1-month postpartum. We characterized maternal HPA-axis function using 10 timed salivary cortisol measurements collected over 2-days (mean: 19.7, range: 14-35 weeks gestation). We used linear mixed models to examine the relationship between Pb biomarkers and cortisol area under the curve (AUC), awakening response (CAR), and diurnal slope.

RESULTS

After adjustment for confounders, women in the highest quintile of BPb concentrations had a reduced CAR (Ratio: -13%; Confidence Interval [CI]: -24, 1, p-value for trend < 0.05) compared to women in the lowest quintile. Tibia/patella Pb concentrations were not associated with CAR, but diurnal cortisol slopes were suggestively flatter among women in the highest patella Pb quantile compared to women in the lowest quantile (Ratio: 14%; CI: -2, 33). BPb and bone Pb concentrations were not associated with cortisol AUC.

CONCLUSIONS

Concurrent blood Pb levels were associated with cortisol awakening response in these pregnant women and this might explain adverse health outcomes associated with Pb. Further research is needed to confirm these results and determine if other environmental chemicals disrupt hypothalamic-pituitary-adrenal-axis function during pregnancy.

Epigenetic Regulation of Infant Neurobehavioral Outcomes

During fetal development and early-infancy, environmental signals can induce epigenetic changes that alter neurobehavioral development and later-life mental health. Several neurodevelopmental genetic diseases influence epigenetic regulatory genes and genomic imprinting. Recently, brain epigenetic marks have been involved in idiopathic neurodevelopmental disorders including autism spectrum disorders (ASD). The placenta is an important regulator of the intrauterine environment that links maternal and fetal nervous systems. Placental epigenetic signatures have been associated with neurodevelopment of healthy newborns quantified through the NICU Network Neurobehavioral Scales (NNNS). Associations have been observed for DNA methylation of genes involved in cortisol (NR3C1, HSD11B), serotonin (HTR2A), and metabolic (LEP) pathways. Dysregulation of imprinted genes and microRNAs has also been associated with neurobehavior assessed by NNNS. Further analysis is needed to characterize the mechanisms by which the epigenome influences neurodevelopment, and the connection between this dysregulation and mental health disorders. In the future, epigenetic marks could serve as functional biomarkers of mental health and cognitive function.

DNA methylation and childhood maltreatment: from animal models to human studies

Childhood maltreatment (CM) has estimated prevalence among Western societies between 10% and 15%. As CM associates with increased risk of several psychiatric disorders, early age of illness onset, increased comorbidity and negative clinical outcome, it imposes a major public health, social and economic impact. Although the clinical consequences of CM are well characterized, a major challenge remains to understand how negative early-life events can affect brain function over extended periods of time. We review here both animal and human studies indicating that the epigenetic mechanism of DNA methylation is a crucial mediator of early-life experiences, thereby maintaining life-long neurobiological sequelae of CM, and strongly determining psychopathological risk.

Epigenetic mechanisms in fetal origins of health and disease

Early life environment predicts future health. The initial precedents and research focus on this concept arose out of historical events. However, this concept continues to be relevant as evidenced by the recent Chinese famine and the evidence of racial disparities in the United States. The latter allows us to introduce the "life course model" and "weathering" as relevant epigenetic phenomena. We then review the molecular components of environmental epigenetics. We subsequently present glucocorticoid receptor biology as a paradigm that involves all of the components. Finally, we suggest that environmental epigenetics are a key component of the future of personalized medicine.

Sex-specific associations between placental leptin promoter DNA methylation and infant neurobehavior

BACKGROUND

Leptin (LEP) is a hormone central for energy homeostasis and has been implicated in neurodevelopment. This adipokine is produced by the placenta and is epigenetically regulated by promoter DNA methylation. Recent evidence has suggested a role for LEP in behavioral development. In this study, we investigated associations between profiles of human newborn neurobehavior and placental LEP DNA methylation.

METHODS

We determined LEP promoter methylation in 444 placental samples from healthy term infants and measured LEP gene expression in a random subset of these samples. Infant neurobehavior was assessed with the NICU Network Neurobehavioral Scales (NNNS) and we examined the relationship between LEP promoter methylation and profiles of infant neurobehavior derived from these scores generated using a hierarchical model-based clustering method.

RESULTS

LEP methylation is negatively correlated with gene expression only in placentas from male infants (r=-0.6, P=0.006). A 10% increase in LEP DNA methylation was associated with membership in a profile of infant neurobehavior marked by increased lethargy and hypotonicity (OR=1.9; 95% CI: 1.07-3.4), and consistently with reduced risk of membership in a profile characterized by decreased lethargy and hypotonicity (OR=0.54; 95% CI: 0.3-0.94) only in male infants (n=223). No statistically significant associations were observed amongst female infants.

DISCUSSION

These results suggest that increased placental LEP DNA methylation, related to reduced expression, may play a role in human newborn neurodevelopment, particularly in reactivity to various stimuli, but that these effects may be sexually dimorphic.

Global and gene-specific DNA methylation across multiple tissues in early infancy: implications for children's health research

An increasing number of population studies are assessing epigenetic variation in relation to early-life outcomes in tissues accessible to epidemiologic researchers. Epigenetic mechanisms are highly tissue specific, however, and it is unclear whether the variation observed in one of the tissue types is representative of other sources or whether the variation in DNA methylation is distinct, reflecting potential functional differences across tissues. To assess relations between DNA methylation in various samples from newborns and children in early infancy, we measured promoter or gene-body DNA methylation in matched term placenta, cord blood, and 3-6 mo saliva samples from 27 unrelated infants enrolled in the Rhode Island Child Health Study. We investigated 7 gene loci (KLF15, NR3C1, LEP, DEPTOR, DDIT4, HSD11B2, and CEBPB) and global methylation, using repetitive region LINE-1 and ALUYb8 sequences. We observed a great degree of interlocus, intertissue, and interindividual epigenetic variation in most of the analyzed loci. In correlation analyses, only cord blood NR3C1 promoter methylation correlated negatively with methylation in saliva. We conclude that placenta, cord blood, and saliva cannot be used as a substitute for one another to evaluate DNA methylation at these loci during infancy. Each tissue has a unique epigenetic signature that likely reflects their differential functions. Future studies should consider the uniqueness of these features, to improve epigenetic biomarker discovery and translation.

The roles of DNA methylation of NR3C1 and 11β-HSD2 and exposure to maternal mood disorder in utero on newborn neurobehavior

Exposure to maternal mood disorder in utero may program infant neurobehavior via DNA methylation of the glucocorticoid receptor (NR3C1) and 11β-hydroxysteroid dehydrogenase type 2 ( 11β-HSD-2), two placental genes that have been implicated in perturbations of the hypothalamic pituitary adrenocortical (HPA) axis. We tested the relations among prenatal exposure to maternal depression or anxiety, methylation of exon 1F of NR3C1 and 11β-HSD-2, and newborn neurobehavior. Controlling for relevant covariates, infants whose mothers reported depression during pregnancy and showed greater methylation of placental NR3C1 CpG2 had poorer self-regulation, more hypotonia, and more lethargy than infants whose mothers did not report depression. On the other hand, infants whose mothers reported anxiety during pregnancy and showed greater methylation of placental 11β-HSD-2 CpG4 were more hypotonic compared with infants of mothers who did not report anxiety during pregnancy. Our results support the fetal programming hypothesis and suggest that fetal adjustments to cues from the intrauterine environment, in this case an environment that could be characterized by increased exposure to maternal cortisol, may lead to poor neurodevelopmental outcomes.

Glucocorticoid receptor gene expression and promoter CpG modifications throughout the human brain

Glucocorticoids and the glucocorticoid (GR) and mineralocorticoid (MR) receptors have been implicated in many processes, particularly in negative feedback regulation of the hypothalamic-pituitary-adrenal axis. Epigenetically programmed GR alternative promoter usage underlies transcriptional control of GR levels, generation of GR 3' splice variants, and the overall GC response in the brain. No detailed analysis of GR first exons or GR transcript variants throughout the human brain has been reported. Therefore we investigated post mortem tissues from 28 brain regions of 5 individuals. GR first exons were expressed throughout the healthy human brain with no region-specific usage patterns. First exon levels were highly inter-correlated suggesting that they are co-regulated. GR 3' splice variants (GRα and GR-P) were equally distributed in all regions, and GRβ expression was always low. GR/MR ratios showed significant differences between the 28 tissues with the highest ratio in the pituitary gland. Modification levels of individual CpG dinucleotides, including 5-mC and 5-hmC, in promoters 1D, 1E, 1F, and 1H were low, and diffusely clustered; despite significant heterogeneity between the donors. In agreement with this clustering, sum modification levels rather than individual CpG modifications correlated with GR expression. Two-way ANOVA showed that this sum modification was both promoter and brain region specific, but that there was however no promoter*tissue interaction. The heterogeneity between donors may however hide such an interaction. In both promoters 1F and 1H modification levels correlated with GRα expression suggesting that 5-mC and 5-hmC play an important role in fine tuning GR expression levels throughout the brain.

Prenatal substance exposure: neurobiologic organization at 1 month

OBJECTIVE

To examine the autonomic nervous system and neurobehavioral response to a sustained visual attention challenge in 1-month-old infants with prenatal substance exposure.

STUDY DESIGN

We measured heart rate, respiratory sinus arrhythmia, and neurobehavior during sustained visual orientation tasks included in the Neonatal Intensive Care Unit Network Neurobehavioral Scale in 1129 1-month-old infants with prenatal substance exposure. Four groups were compared: infants with prenatal cocaine and opiate exposure, infants with cocaine exposure, infants with opiate exposure, and infants with exposure to other substances (ie, alcohol, marijuana, and tobacco).

RESULTS

The infants with prenatal exposure to both cocaine and opiates had the highest heart rates and lowest levels of respiratory sinus arrhythmia during a sustained visual attention challenge compared with the other 3 groups. Infants with prenatal cocaine and opiate exposure had poorer quality of movement and more hypertonicity during the Neonatal Intensive Care Unit Network Neurobehavioral Scale examination. They also had more nonoptimal reflexes and stress/abstinence signs compared with infants with prenatal exposure to cocaine only and those with prenatal exposure to alcohol, tobacco, and marijuana.

CONCLUSION

Problems with arousal regulation were identified in infants with prenatal substance exposure. Autonomic dysregulation has been implicated as a mechanism by which these difficulties occur. Our results suggest that infants with prenatal exposure to both cocaine and opiates have the greatest autonomic response to the challenge of a sustained visual attention task, possibly putting these infants at risk for problems associated with physiologic and behavioral regulation, a necessary prerequisite for early learning.

Epigenetic basis for the development of depression in children

The growing field of epigenetics and human behavior affords an unprecedented opportunity to discover molecular underpinnings of mental health disorders and pave the way for the development of preventive intervention programs. Maternal depression during pregnancy is a serious public health issue and leads to a 4-fold increase in the likelihood that the child will develop depression. We describe how mood disorders, particularly depression, may be shaped by early life stress, programming, and epigenetic processes and pathways showing how these processes could lead to depression in childhood. Implications of this approach to the study of mental health disorders for preventive interventions are discussed.

Grandchild of the NBAS: the NICU network neurobehavioral scale (NNNS): a review of the research using the NNNS

A review of the research on the NICU Network Neurobehavioral Scale (NNNS) is presented. The NNNS has good psychometric properties and reliability. Standardized norms are available for it. It was found to be sensitive to a wide variety of medical, exposure, and demographic variables and has robust predictive validity. It will be useful for nurses for detecting neurobehavioral problems and management of the young infant.

Placental HTR2A methylation is associated with infant neurobehavioral outcomes

The serotonin receptor, HTR2A, exhibits placental expression and function and can be controlled through DNA methylation. The relationship between methylation of HTR2A in the placenta and neurodevelopmental outcomes, evaluated using the NICU Network Neurobehavioral Scales (NNNS), was assessed in newborn infants (n = 444). HTR2A methylation was significantly higher in males and marginally higher in infants whose mothers reported tobacco use during pregnancy. Controlling for confounding variables, HTR2A methylation was negatively associated with infant quality of movement (p = 0.05) and positively associated with infant attention (p = 0.0001). These results suggest that methylation of the HTR2A gene can be biologically and environmentally modulated and is associated with key measures of neurodevelopment.

Early onset pre-eclampsia is associated with altered DNA methylation of cortisol-signalling and steroidogenic genes in the placenta

Placental cortisol is inactivated in normotensive pregnancies, but is frequently present in pre-eclampsia associated placentae. Since glucocorticoids are strongly associated with the programming of long-term health, we assessed DNA methylation of genes involved in cortisol signalling and bioavailability, and hormonal signalling in the placenta of normotensive and hypertensive pregnancies. Candidate genes/CpG sites were selected through analysis of Illumina Infinium HumanMethylation450 BeadChip array data on control (n = 19) and early onset pre-eclampsia (EOPET; n = 19) placental samples. DNA methylation was further quantified by bisulfite pyrosequencing in a larger cohort of control (n = 111) cases, in addition to EOPET (n = 19), late onset pre-eclampsia (LOPET; n = 18) and normotensive intrauterine growth restriction (nIUGR; n = 13) cases. DNA methylation (percentage points) was increased at CpG sites within genes encoding the glucocorticoid receptor (NR3C1 exon 1D promoter; +8.46%; P<0.01) and corticotropin releasing hormone (CRH) binding protein (CRHBP intron 3; +9.14%; P<0.05), and decreased within CRH (5' UTR; -4.30%; P = 0.11) in EOPET-associated placentae, but not in LOPET nor nIUGR cases, compared to controls. Differential DNA methylation was not observed among groups at the 11β-hydroxysteroid dehydrogenase type 2 (HSD11B2) gene promoter. Significant hypomethylation was observed in pre-eclampsia but not nIUGR placentae for steroidogenic genes, including CYP11A1 (exon1; EOPET; -9.66%; P<0.00001, and LOPET; -5.77%; P<0.001), 3β-hydroxy-delta-5-steroid dehydrogenase type 1 (HSD3B1 exon 2; EOPET; -12.49%; P<0.00001, and LOPET; -6.88%; P<0.001), TEA domain family member 3 (TEAD3 intron 1; EOPET; -12.56%; P<0.00001) and CYP19 (placental-specific exon 1.1 promoter; EOPET; -10.62%, P<0.0001). These data represent dysregulation of the placental epigenome in pre-eclampsia related to genes involved in maintaining the hormonal environment during pregnancy and highlights particular susceptibility in the early onset syndrome.

Epigenetic regulation of the glucocorticoid receptor promoter 1(7) in adult rats

Regulation of glucocorticoid receptor (GR) levels is an important stress adaptation mechanism. Transcription factor Nfgi-a and environmentally induced Gr promoter 1 7 methylation have been implicated in fine-tuning the expression of Gr 1 7 transcripts. Here, we investigated Gr promoter 1 7 methylation and Gr 1 7 expression in adult rats exposed to either acute or chronic stress paradigms. A strong negative correlation was observed between the sum of promoter-wide methylation levels and Gr 1 7 transcript levels, independent of the stressor. Methylation of individual sites did not, however, correlate with transcript levels. This suggested that promoter 1 7 was directly regulated by promoter-wide DNA methylation. Although acute stress increased Ngfi-a expression in the hypothalamic paraventricular nucleus (PVN), Gr 1 7 transcript levels remained unaffected despite low methylation levels. Acute stress had little effect on these low methylation levels, except at four hippocampal CpGs. Chronic stress altered the corticosterone response to an acute stressor. In the adrenal and pituitary glands, but not in the brain, this was accompanied by an increase in methylation levels in orchestrated clusters rather than individual CpGs. PVN methylation levels, unaffected by acute or chronic stress, were significantly more variable within- than between-groups, suggesting that they were instated probably during the perinatal period and represent a pre-established trait. Thus, in addition to the known perinatal programming, the Gr 1 7 promoter is epigenetically regulated by chronic stress in adulthood, and retains promoter-wide tissue-specific plasticity. Differences in methylation susceptibility between the PVN in the perinatal period and the peripheral HPA axis tissues in adulthood may represent an important "trait" vs. "state" regulation of the Gr gene.