Epigenetic effects of glucocorticoids

In utero glucocorticoid exposure reduces fetal skeletal muscle mass in rats independent of effects on maternal nutrition

Maternal stress and undernutrition can occur together and expose the fetus to high glucocorticoid (GLC) levels during this vulnerable period. To determine the consequences of GLC exposure on fetal skeletal muscle independently of maternal food intake, groups of timed-pregnant Sprague-Dawley rats (n = 7/group) were studied: ad libitum food intake (control, CON); ad libitum food intake with 1 mg dexamethasone/l drinking water from embryonic day (ED)13 to ED21 (DEX); pair-fed (PF) to DEX from ED13 to ED21. On ED22, dams were injected with [(3)H]phenylalanine for measurements of fetal leg muscle and diaphragm fractional protein synthesis rates (FSR). Fetal muscles were analyzed for protein and RNA contents, [(3)H]phenylalanine incorporation, and MuRF1 and atrogin-1 (MAFbx) mRNA expression. Fetal liver tyrosine aminotransferase (TAT) expression was quantified to assess fetal exposure to GLCs. DEX treatment reduced maternal food intake by 13% (P < 0.001) and significantly reduced placental mass relative to CON and PF dams. Liver TAT expression was elevated only in DEX fetuses (P < 0.01). DEX muscle protein masses were 56% and 70% than those of CON (P < 0.01) and PF (P < 0.05) fetuses, respectively; PF muscles were 80% of CON (P < 0.01). Muscle FSR decreased by 35% in DEX fetuses (P < 0.001) but were not different between PF and CON. Only atrogin-1 expression was increased in DEX fetus muscles. We conclude that high maternal GLC levels and inadequate maternal food intake impair fetal skeletal muscle growth, most likely through different mechanisms. When combined, the effects of decreased maternal intake and maternal GLC intake on fetal muscle growth are additive.

Advances in tryptophan hydroxylase-2 gene expression regulation: new insights into serotonin-stress interaction and clinical implications

Serotonin (5-HT) modulates the stress response by interacting with the hormonal hypothalamic-pituitary-adrenal (HPA) axis and neuronal sympathetic nervous system (SNS). Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in 5-HT biosynthesis, and the recent identification of a second, neuron-specific TPH isoform (TPH2) opened up a new area of research. While TPH2 genetic variance has been linked to numerous behavioral traits and disorders, findings on TPH2 gene expression have not only reinforced, but also provided new insights into, the long-recognized but not yet fully understood 5-HT-stress interaction. In this review, we summarize advances in TPH2 expression regulation and its relevance to the stress response and clinical implications. Particularly, based on findings on rhesus monkey TPH2 genetics and other relevant literature, we propose that: (i) upon activation of adrenal cortisol secretion, the cortisol surge induces TPH2 expression and de novo 5-HT synthesis; (ii) the induced 5-HT in turn inhibits cortisol secretion by modulating the adrenal sensitivity to ACTH via the suprachiasmatic nuclei (SCN)-SNS-adrenal system, such that it contributes to the feedback inhibition of cortisol production; (iii) basal TPH2 expression or 5-HT synthesis, as well as early-life experience, influence basal cortisol primarily via the hormonal HPA axis; and (iv) 5'- and 3'-regulatory polymorphisms of TPH2 may differentially influence the stress response, presumably due to their differential roles in gene expression regulation. Our increasing knowledge of TPH2 expression regulation not only helps us better understand the 5-HT-stress interaction and the pathophysiology of neuropsychiatric disorders, but also provides new strategies for the treatment of stress-associated diseases.

Stress and the HPA axis: role of glucocorticoids in alcohol dependence

Stress has long been suggested to be an important correlate of uncontrolled drinking and relapse. An important hormonal response system to stress-the hypothalamic-pituitary-adrenal (HPA) axis-may be involved in this process, particularly stress hormones known as glucocorticoids and primarily cortisol. The actions of this hormone system normally are tightly regulated to ensure that the body can respond quickly to stressful events and return to a normal state just as rapidly. The main determinants of HPA axis activity are genetic background, early-life environment, and current life stress. Alterations in HPA axis regulation are associated with problematic alcohol use and dependence; however, the nature of this dysregulation appears to vary with respect to stage of alcohol dependence. Much of this research has focused specifically on the role of cortisol in the risk for, development of, and relapse to chronic alcohol use. These studies found that cortisol can interact with the brain's reward system, which may contribute to alcohol's reinforcing effects. Cortisol also can influence a person's cognitive processes, promoting habit-based learning, which may contribute to habit formation and risk of relapse. Finally, cortisol levels during abstinence may be useful clinical indicators of relapse vulnerability in alcohol-dependent people.

Neurogenetics and Epigenetics in Impulsive Behaviour: Impact on Reward Circuitry

Adverse, unfavourable life conditions, particularly during early life stages and infancy, can lead to epigenetic regulation of genes involved in stress-response, behavioral disinhibition, and cognitive-emotional systems. Over time, the ultimate final outcome can be expressed through behaviors bedeviled by problems with impulse control, such as eating disorders, alcoholism, and indiscriminate social behavior. While many reward gene polymorphisms are involved in impulsive behaviors, a polymorphism by itself may not translate to the development of a particular behavioral disorder unless it is impacted by epigenetic effects. Brain-derived neurotrophic factor (BDNF) affects the development and integrity of the noradrenergic, dopaminergic, serotonergic, glutamatergic, and cholinergic neurotransmitter systems, and plasma levels of the neurotrophin are associated with both cognitive and aggressive impulsiveness. Epigenetic mechanisms associated with a multitude of environmental factors, including premature birth, low birth weight, prenatal tobacco exposure, non-intact family, young maternal age at birth of the target child, paternal history of antisocial behavior, and maternal depression, alter the developmental trajectories for several neuropsychiatric disorders. These mechanisms affect brain development and integrity at several levels that determine structure and function in resolving the final behavioral expressions.

Targeting epigenetic mechanisms for pain relief

Epigenetic changes are chemical modifications to chromatin that modulate gene activity without altering the DNA sequence. While research on epigenetics has grown exponentially over the past few years, very few studies have investigated epigenetic mechanisms in relation to pain states. However, epigenetic mechanisms are crucial to memory formation that requires similar synaptic plasticity to pain processing, indicating that they may play a key role in the control of pain states. This article reviews the early evidence suggesting that epigenetic mechanisms are engaged after injury and in chronic pain states, and that drugs used clinically to target the epigenetic machinery for the treatment of cancer might be useful for the management of chronic pain.

Developmental programming of early brain and behaviour development and mental health: a conceptual framework

The Developmental Origins of Health and Disease (DOHaD) hypothesis studies the short- and long-term consequences of the conditions of the developmental environment for phenotypic variations in health and disease. Central to this hypothesis is the idea of interdependence of developmental influences, genes, and environment. Developmental programming effects are mediated by alterations in fundamental life functions, and the most enduring effects seem to occur if the main regulatory instances of the organ - the (epi)genome and the brain - are affected. Some new insights in the role of chromatin, in cellular development and differentiation, and neural plasticity from the field of epigenetics are introduced, followed by a section on epigenetics and brain development. It is proposed to extend the DOHaD hypothesis into the 'Developmental Origins of Behaviour, Health, and Disease' (DOBHaD) concept. Pregnancy and the early postnatal period are times of both great opportunity and considerable risk, and their influence can extend over a lifetime. The DOBHaD hypothesis opens fundamental new perspectives on preventing diseases and disorders.

Sex differences in prenatal epigenetic programming of stress pathways

Maternal stress experience is associated with neurodevelopmental disorders including schizophrenia and autism. Recent studies have examined mechanisms by which changes in the maternal milieu may be transmitted to the developing embryo and potentially translated into programming of the epigenome. Animal models of prenatal stress have identified important sex- and temporal-specific effects on offspring stress responsivity. As dysregulation of stress pathways is a common feature in most neuropsychiatric diseases, molecular and epigenetic analyses at the maternal-embryo interface, especially in the placenta, may provide unique insight into identifying much-needed predictive biomarkers. In addition, as most neurodevelopmental disorders present with a sex bias, examination of sex differences in the inheritance of phenotypic outcomes may pinpoint gene targets and specific windows of vulnerability in neurodevelopment, which have been disrupted. This review discusses the association and possible contributing mechanisms of prenatal stress in programming offspring stress pathway dysregulation and the importance of sex.

Prenatal betamethasone exposure has sex specific effects in reversal learning and attention in juvenile baboons

OBJECTIVE

We investigated effects of 3 weekly courses of fetal betamethasone (βM) on motivation and cognition in juvenile baboon offspring utilizing the Cambridge Neuropsychological Test Automated Battery.

STUDY DESIGN

Pregnant baboons (Papio species) received 2 injections of saline control or 175 μg/kg βM 24 hours apart at 0.6, 0.65, and 0.7 gestation. Offspring (saline control female, n = 7 and saline control male, n = 6; βM female [FβM], n = 7 and βM male [MβM], n = 5) were studied at 2.6-3.2 years with a progressive ratio test for motivation, simple discriminations and reversals for associative learning and rule change plasticity, and an intra/extradimensional set-shifting test for attention allocation.

RESULTS

βM exposure decreased motivation in both sexes. In intra/extradimensional testing, FβM made more errors in the simple discrimination reversal (mean difference of errors [FβM - MβM] = 20.2 ± 9.9; P ≤ .05), compound discrimination (mean difference of errors = 36.3 ± 17.4; P ≤ .05), and compound reversal (mean difference of errors = 58 ± 23.6; P < .05) stages as compared to the MβM offspring.

CONCLUSION

This central nervous system developmental programming adds growing concerns of long-term effects of repeated fetal synthetic glucocorticoid exposure. In summary, behavioral effects observed show sex-specific differences in resilience to multiple fetal βM exposures.

Effects of early life stress on neuroendocrine and neurobehavior: mechanisms and implications

Evidence continues to mount that adverse experiences early in life have an impact on brain functions. Early life stress can program the development of the hypothalamic-pituitary-adrenal axis and cause alterations of neurochemistry and signaling pathways involved in regulating neuroplasticity, with resultant neurobehavioral changes. Early life experiences and genetic factors appear to interact in determining the individual vulnerability to mental health disorders. We reviewed the effects of early life stress on neuroendocrine regulation and the relevance to neurobehavioral development.

Child health, developmental plasticity, and epigenetic programming

Plasticity in developmental programming has evolved in order to provide the best chances of survival and reproductive success to the organism under changing environments. Environmental conditions that are experienced in early life can profoundly influence human biology and long-term health. Developmental origins of health and disease and life-history transitions are purported to use placental, nutritional, and endocrine cues for setting long-term biological, mental, and behavioral strategies in response to local ecological and/or social conditions. The window of developmental plasticity extends from preconception to early childhood and involves epigenetic responses to environmental changes, which exert their effects during life-history phase transitions. These epigenetic responses influence development, cell- and tissue-specific gene expression, and sexual dimorphism, and, in exceptional cases, could be transmitted transgenerationally. Translational epigenetic research in child health is a reiterative process that ranges from research in the basic sciences, preclinical research, and pediatric clinical research. Identifying the epigenetic consequences of fetal programming creates potential applications in clinical practice: the development of epigenetic biomarkers for early diagnosis of disease, the ability to identify susceptible individuals at risk for adult diseases, and the development of novel preventive and curative measures that are based on diet and/or novel epigenetic drugs.

Glucocorticoids and stress‐related depression: an evaluation of biological mechanisms and the potential for new therapeutics

Purpose

Principles of epigenesis that provide a foundation for research into chronic medical disorders are increasingly being applied in the context of mental health. The purpose of this paper is to consider recent research evidence for epigenetic influences in the pathogenesis of depression, and the putative links with stress biology during exposure to chronic stress, with the aim of placing this into a context of potential new therapeutics.

Design/methodology/approach

Substantive reviews published during the last ten years were identified in a search of the Pubmed database in September 2010 using the terms “epigenetics” or “epigenesis” with “mental health”, “mood disorder”, “depression”, stress', “chronic stress” or “environment”, supplemented by hand‐searching of citations in the reviews.

Findings

Epigenetic mechanisms are both heritable and acquired, and their impact on the underlying genome helps explain individual vulnerability and patterns of occurrence of depression.

Originality/value

The paper shows that this relatively new field of research is in its infancy, and the influence of adverse environments (i.e. stressors) on genetic/epigenetic predisposition has promise for the advent of novel therapeutics based on epigenetic manipulation.

The prefrontal-limbic network in depression: Modulation by hypothalamus, basal ganglia and midbrain

The anterior cingulate cortex, amygdala and hippocampus form part of an interconnected prefrontal neocortical and limbic archicortical network that is dysregulated in major depressive disorders (MDD). Modulation of this prefrontal-limbic network (PLN) is principally through the hypothalamus, basal ganglia and midbrain. Here the likely mechanisms by which these modulations are affected are described and the implications of their failure for depression associated with suicidal diathesis, late-life and psychoses discussed.

Joining the dots: neurobiological links in a functional analysis of depression

Depression is one of the major contributors to the Total Disease Burden and afflicts about one-sixth of Western populations. One of the most effective treatments for depression focuses upon analysis of causal chains in overt behaviour, but does not include brain-related phenomena as steps along these causal pathways. Recent research findings regarding the neurobiological concomitants of depressive behaviour suggest a sequence of structural and functional alterations to the brain which may also produce a beneficial outcome for the depressed individual--that of adaptive withdrawal from uncontrollable aversive stressors. Linking these brain-based explanations to models of observable contingencies for depressive behaviour can provide a comprehensive explanation of how depressive behaviour occurs and why it persists in many patients.

Effects of perinatal cocaine exposure on open field behavior and the response to corticotropin releasing hormone (CRH) in rat offspring

Previous reports indicate that prenatal cocaine exposure alters specific behaviors and hypothalamic-pituitary-adrenal axis (HPA) function in the offspring. In most previous studies, cocaine was given via subcutaneous injections. However intravenous administration more closely mimics human cocaine abuse during pregnancy. Therefore, we investigated the effects of prenatal cocaine exposure via intravenous injection to the mothers on open field behavior and HPA axis function of the offspring. We hypothesized that prenatal cocaine exposure decreases immobility in a novel environment, and enhances the HPA response to stress. Dams received cocaine (COC) or vehicle (control, CON) intravenously from gestation day 8 to postnatal day (PD) 5. Behaviors were recorded in the open field on PD 28 (weanlings). As expected, perinatally cocaine-exposed offspring spent less time immobile and had a longer latency to entering the center zone. No other behavioral activities were different between the groups. On PD 43-50, adolescent male and female offspring received either corticotropin releasing hormone (CRH) or saline intravenously. Plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT) levels were determined before, and up to 60 min after injection. COC-exposed offspring of both sexes had higher basal CORT levels. Prenatal cocaine enhanced the CORT response to CRH/saline injections up to 60 min in males but not in females. These novel results show that perinatal administration of cocaine in a manner that most closely mimics human cocaine use has long-term effects on the offspring's behavioral response to stress and on HPA axis functions.

Lactobacillus rhamnosus GR-1 stimulates colony-stimulating factor 3 (granulocyte) (CSF3) output in placental trophoblast cells in a fetal sex-dependent manner

Bacterial vaginosis is associated with a 1.4-fold increased risk of preterm birth. We have shown previously that Lactobacillus rhamnosus GR-1 supernatant up-regulates interleukin 10 and down-regulates tumor necrosis factor-alpha output in lipopolysaccharide (LPS)-treated human primary placenta cultures in a fetal sex-dependent manner. We hypothesize that lactobacilli also exert their anti-inflammatory effect by up-regulation of colony-stimulating factor 3 (granulocyte) (CSF3), which is secreted from both immune and placental trophoblast cells, and that this activity is dependent on the sex of the fetus. Placental trophoblast cells were isolated from term elective cesarean section placentae using a Percoll gradient and separated from CD45(+) cells using magnetic purification. Cells were treated with LPS in the presence or absence of pretreatments with L. rhamnosus GR-1 supernatant or chemical inhibitors of the intracellular signaling pathways. Phosphorylations of mitogen-activated protein kinase 14 (MAPK14, previously known as p38) and signal transducer and activator of transcription (STAT) 3 were measured by Western blot analysis, and levels of CSF3 were determined by ELISA. CSF3 output was increased only in the placental trophoblast cells of female fetuses treated with LPS, GR-1 supernatant, and a combination of both treatments. The GR-1 supernatant up-regulated the phosphorylation of STAT3 and MAPK14. CSF3 output was inhibited by both Janus kinases (JAK) and MAPK14 inhibitors. None of the treatments was able to increase CSF3 output in either the pure trophoblast or the CD45(+) cell preparations alone. These results suggest an underlying mechanism for the sex difference in incidence of preterm birth and provide potential evidence for a therapeutic benefit of lactobacilli in reducing the risk of preterm labor.

Epigenetic changes in the hypothalamic proopiomelanocortin and glucocorticoid receptor genes in the ovine fetus after periconceptional undernutrition

Maternal food restriction is associated with the development of obesity in offspring. This study examined how maternal undernutrition in sheep affects the fetal hypothalamic glucocorticoid receptor (GR) and the appetite-regulating neuropeptides, proopiomelanocortin (POMC) and neuropeptide Y, which it regulates. In fetuses from ewes undernourished from -60 to +30 d around conception, there was increased histone H3K9 acetylation (1.63-fold) and marked hypomethylation (62% decrease) of the POMC gene promoter but no change in POMC expression. In the same group, acetylation of histone H3K9 associated with the hypothalamic GR gene was increased 1.60-fold and the GR promoter region was hypomethylated (53% decrease). In addition, there was a 4.7-fold increase in hypothalamic GR expression but no change in methylation of GR gene expression in the anterior pituitary or hippocampus. Interestingly, hypomethylation of both POMC and GR promoter markers in fetal hypothalami was also identified after maternal undernutrition from -60 to 0 d and -2 to +30 d. In comparison, the Oct4 gene, was hypermethylated in both control and underfed groups. Periconceptional undernutrition is therefore associated with marked epigenetic changes in hypothalamic genes. Increase in GR expression in the undernourished group may contribute to fetal programming of a predisposition to obesity, via altered GR regulation of POMC and neuropeptide Y. These epigenetic changes in GR and POMC in the hypothalamus may also predispose the offspring to altered regulation of food intake, energy expenditure, and glucose homeostasis later in life.

Vulnerability to stroke: implications of perinatal programming of the hypothalamic-pituitary-adrenal axis

Chronic stress is capable of exacerbating each major, modifiable, endogenous risk factor for cerebrovascular and cardiovascular disease. Indeed, exposure to stress can increase both the incidence and severity of stroke, presumably through activation of the hypothalamic-pituitary-adrenal (HPA) axis. Now that characterization of the mechanisms underlying epigenetic programming of the HPA axis is well underway, there has been renewed interest in examining the role of early environment on the evolution of health conditions across the entire lifespan. Indeed, neonatal manipulations in rodents that reduce stress responsivity, and subsequent life-time exposure to glucocorticoids, are associated with a reduction in the development of neuroendocrine, neuroanatomical, and cognitive dysfunctions that typically progress with age. Although improved day to day regulation of the HPA axis also may be accompanied by a decrease in stroke risk, evidence from rodent studies suggest that an associated cost could be increased susceptibility to inflammation and neuronal death in the event that a stroke does occur and the individual is exposed to persistently elevated corticosteroids. Given its importance in regulation of health and disease states, any long-term modulation of the HPA axis is likely to be associated with both benefits and potential risks. The goals of this review article are to examine (1) the clinical and experimental data suggesting that neonatal experiences can shape HPA axis regulation, (2) the influence of stress and the HPA axis on stroke incidence and severity, and (3) the potential for neonatal programming of the HPA axis to impact adult cerebrovascular health.

Neurobiological Pathways between Chronic Stress and Depression: Dysregulated Adaptive Mechanisms?

Stress-related diseases have been predicted to become major contributors to the Global Disease Burden within the next 20 years. Of these, depression is one of the principal identifiable sources of concern for public mental health, and has been hypothesized to be an outcome of prolonged stress. Examination of the hyper-responsiveness of the Hypothalamic-Pituitary-Adrenal axis, consequent elevated serum cortisol, plus the effects of this upon brain structure and function, provides a model for understanding how chronic stress may be a causal vector in the development of depression. Evidence from studies of the effectiveness of antidepressants aimed at reducing cortisol within depressed patients supports this model and suggests avenues for future research and treatment of stress-induced depression.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Deployment-related severe fatigue with depressive symptoms is associated with increased glucocorticoid binding to peripheral blood mononuclear cells

Severe fatigue and co-morbid depressive symptoms are frequently reported by recently deployed military personnel. Stress can induce lasting changes in the negative feedback regulation of the hypothalamic-pituitary-adrenal axis (HPA-axis) and the regulation of the immune system by cortisol. Since these actions of cortisol are modulated via glucocorticoid receptors (GR), we investigated the effect of deployment and of deployment-related fatigue on glucocorticoid binding to peripheral blood mononuclear cells (PBMCs) in a prospective design. Psychological assessments and blood sample collection took place before and one and six months after deployment. Participants were selected from a larger group and assigned to three groups based on their level of fatigue and depressive symptoms six months after deployment. We compared fatigued participants without depressive symptoms (n=21), fatigued participants with depressive symptoms (n=14) and non-fatigued participants without depressive symptoms (n=21). Fatigued participants with depressive symptoms at six months after deployment had higher glucocorticoid binding to PMBCs than the other two groups at all three time points. Notably, this difference was already present before deployment. There was no effect of deployment on glucocorticoid binding to PBMCs. The observed differences in glucocorticoid binding were not related to pre-existing group differences in psychological symptoms. No group differences were observed in the composition of the PBMC population and plasma cortisol levels. These results indicate that high glucocorticoid binding to PBMCs might represent a vulnerability factor for the development of severe fatigue with depressive symptoms after a sustained period of stress, such as deployment.