Hormonally mediated epigenetic changes to steroid receptors in the developing brain: implications for sexual differentiation

Sex-dependent effect of sublethal copper concentrations on de novo cholesterol synthesis in astrocytes and their possible links to variations in cholesterol and amyloid precursor protein levels in neuronal membranes

BACKGROUND

Cholesterol (Cho) is an essential lipophilic molecule in cells; however, both its decrease and its increase may favor the development of neurological diseases such as Alzheimer's disease (AD). Although copper (Cu) is an essential trace metal for cells, the increased plasma concentration of its free form has been linked with AD development and severity. AD affects aged people, but its prevalence and severity are higher in women than in men. We have previously shown that Cu promotes Cho de novo synthesis in immature neurons as well as increased Cho in membrane rafts and Aβ levels in culture medium, but there are no results yet regarding sex differences in the effects of sublethal Cu exposure on Cho de novo synthesis.

METHODS

We examined the potential sex-specific impact of sublethal Cu concentrations on de novo Cho synthesis in primary cultures of male and female astrocytes. We also explored whether this had any correlation with variations in Cho and APP levels within neuronal membrane rafts.

RESULTS

Flow cytometry analysis demonstrated that Cu treatment leads to a greater increase in ROS levels in female astrocytes than in males. Furthermore, through RT-PCR analysis, we observed an upregulation of SREBP-2 and HMGCR. Consistently, we observed an increase in de novo Cho synthesis. Finally, western blot analysis indicated that the levels of ABCA1 increase after Cu treatment, accompanied by a higher release of radiolabeled Cho and an elevation in Cho and APP levels in neuronal membrane rafts. Importantly, all these results were significantly more pronounced in female astrocytes than in males.

CONCLUSIONS

Our findings confirm that Cu stimulates Cho synthesis in astrocytes, both in a ROS-dependent and -independent manner. Moreover, female astrocytes displayed elevated levels of HMGCR, and de novo Cho synthesis compared to males following TBH and Cu treatments. This corresponds with higher levels of Cho released into the culture medium and a more significant Cho and APP rise within neuronal rafts. We consider that the increased risk of AD in females partly arises from sex-specific responses to metals and/or exogenous substances, impacting key enzyme regulation in various biochemical pathways, including HMGCR.

Multigenerational impacts of EE2 on reproductive fitness and immune competence of marine medaka

Estrogenic endocrine disrupting chemicals (EEDC) have been suspected to impact offspring in a transgenerational manner via modifications of the germline epigenome in the directly exposed generations. A holistic assessment of the concentration/ exposure duration-response, threshold level, and critical exposure windows (parental gametogenesis and embryogenesis) for the transgenerational evaluation of reproduction and immune compromise concomitantly will inform the overall EEDC exposure risk. We conducted a multigenerational study using the environmental estrogen, 17α-ethinylestradiol (EE2), and the marine laboratory model fish Oryzias melastigma (adult, F0) and their offspring (F1-F4) to identify transgenerationally altered offspring generations and phenotype persistence. Three exposure scenarios were used: short parental exposure, long parental exposure, and a combined parental and embryonic exposure using two concentrations of EE2 (33ng/L, 113ng/L). The reproductive fitness of fish was evaluated by assessing fecundity, fertilization rate, hatching success, and sex ratio. Immune competence was assessed in adults via a host-resistance assay. EE2 exposure during both parental gametogenesis and embryogenesis was found to induce concentration/ exposure duration-dependent transgenerational reproductive effects in the unexposed F4 offspring. Furthermore, embryonic exposure to 113 ng/L EE2 induced feminization of the directly exposed F1 generation, followed by subsequent masculinization of the F2 and F3 generations. A sex difference was found in the transgenerationally impaired reproductive output with F4 females being sensitive to the lowest concentration of EE2 (33 ng/L) upon long-term ancestral parent exposure (21 days). Conversely, F4 males were affected by ancestral embryonic EE2 exposure. No definitive transgenerational impacts on immune competence were identified in male or female offspring. In combination, these results indicate that EEDCs can be transgenerational toxicants that may negatively impact the reproductive success and population sustainability of fish populations.

Epigenetic Modifications by Estrogen and Androgen in Alzheimer's Disease

For the development and maintenance of neuron networks in the brain, epigenetic mechanisms are necessary, as indicated by recent findings. This includes some of the high-order brain processes, such as behavior and cognitive functions. Epigenetic mechanisms could influence the pathophysiology or etiology of some neuronal diseases, altering disease susceptibility and therapy responses. Recent studies support epigenetic dysfunctions in neurodegenerative and psychiatric conditions, such as Alzheimer's disease (AD). These dysfunctions in epigenetic mechanisms also play crucial roles in the transgenerational effects of the environment on the brain and subsequently in the inheritance of pathologies. The possible role of gonadal steroids in the etiology and progression of neurodegenerative diseases, including Alzheimer's disease, has become the subject of a growing body of research over the last 20 years. Recent scientific findings suggest that epigenetic changes, driven by estrogen and androgens, play a vital role in brain functioning. Therefore, exploring the role of estrogen and androgen-based epigenetic changes in the brain is critical for the deeper understanding of AD. This review highlights the epigenetic modifications caused by these two gonadal steroids and the possible therapeutic strategies for AD.

On the Interplay Between the Medicine of Hildegard of Bingen and Modern Medicine: The Role of Estrogen Receptor as an Example of Biodynamic Interface for Studying the Chronic Disease's Complexity

Introduction

Hildegard of Bingen (1098-1179) interpreted the origins of chronic disease highlighting and anticipating, although only in a limited fashion, the importance that complex interactions among numerous genetic, internal milieu and external environmental factors have in determining the disease phenotype. Today, we recognize those factors, capable of mediating the transmission of messages between human body and environment and vice versa, as biodynamic interfaces.

Aim

We analyzed, in the light of modern scientific evidence, Hildegard of Bingen's medical approach and her original humoral theory in order to identify possible insights included in her medicine that could be referred to in the context of modern evidence-based medicine. In particular, the abbess's humoral theory suggests the identification of biodynamic interfaces with sex hormones and their receptors.

Findings

We found that the Hildegardian holistic vision of the organism-environment relationship can actually represent a visionary approach to modern endocrinology and that sex hormones, in particular estrogens, could represent an example of a biodynamic interface. Estrogen receptors are found in regions of the brain involved in emotional and cognitive regulation, controlling the molecular mechanism of brain function. Estrogen receptors are involved in the regulation of the hypothalamic-pituitary-adrenal axis and in the epigenetic regulation of responses to physiological, social, and hormonal stimuli. Furthermore, estrogen affects gene methylation on its own and related receptor promoters in discrete regions of the developing brain. This scenario was strikingly perceived by the abbess in the XIIth century, and depicted as a complex interplay among different humors and flegmata that she recognized to be sex specific and environmentally regulated.

Viewpoint

Considering the function played by hormones, analyzed through the last scientific evidence, and scientific literature on biodynamic interfaces, we could suggest Hildegardian insights and theories as the first attempt to describe the modern holistic, sex-based medicine.

Conclusion

Hildegard anticipated a concept of pathogenesis that sees a central role for endocrinology in sex-specific disease. Furthermore, estrogens and estrogen receptors could represent a good example of molecular interfaces capable of modulating the interaction between the organism internal milieu and the environmental factors.

Neurogenesis in the neonatal rat hippocampus is regulated by sexually dimorphic epigenetic modifiers

Background

Neurogenesis in the hippocampus endures across the lifespan but is particularly prolific during the first postnatal week in the developing rodent brain. The majority of new born neurons are in the dentate gyrus (DG). The number of new neurons born during the first postnatal week in the DG of male rat pups is about double the number in females. In other systems, the rate of cell proliferation is controlled by epigenetic modifications in stem cells. We, therefore, explored the potential impact of DNA methylation and histone acetylation on cell genesis in the developing DG of male and female rats.

Methods

Cell genesis was assessed by quantification of BrdU + cells in the DG of neonatal rats following injections on multiple days. Methylation and acetylation were manipulated pharmacologically by injection of well vetted drugs. DNA methylation, histone acetylation and associated enzyme activity were measured using commercially available colorimetric assays. mRNA was quantified by PCR. Multiple group comparisons were made by one- or two-way ANOVA followed by post-hoc tests controlling for multiple comparisons. Two groups were compared by t test.

Results

We found higher levels of DNA methylation in male DG and treatment with the DNA methylating enzyme inhibitor zebularine reduced the methylation and correspondingly reduced cell genesis. The same treatment had no impact on either measure in females. By contrast, treatment with a histone deacetylase inhibitor, trichostatin-A, increased histone acetylation in the DG of both sexes but increased cell genesis only in females. Females had higher baseline histone deacetylase activity and greater inhibition in response to trichostatin-A treatment. The mRNA levels of the proproliferative gene brain-derived neurotrophic factor were greater in males and reduced by inhibiting both DNA methylation and histone deacetylation only in males.

Conclusions

These data reveal a sexually dimorphic epigenetically based regulation of neurogenesis in the DG but the mechanisms establishing the distinct regulation involving DNA methylation in males and histone acetylation in females is unknown.

Neurogenesis in the dentate gyrus peaks in the early postnatal period and in the laboratory rat is significantly greater in males than females.

Here we report divergent regulation of cell genesis in the neonatal dentate gyrus. DNA methylation is a critical regulator of the higher rates of proliferation in males. Conversely, histone acetylation is essential for cell genesis in females.

Neighborhood Socioeconomic Deprivation and Mortality in Children with Central Nervous System Tumors

BACKGROUND

Although there is evidence of socioeconomic disparities in survival of children diagnosed with central nervous system (CNS) tumors, the impact of neighborhood socioeconomic deprivation on the survival of these malignancies has not been adequately studied. We investigated the association between area deprivation index (ADI), a measure of neighborhood socioeconomic disadvantage, and pediatric CNS tumor survival.

METHODS

Demographic and clinical characteristics, geocoded addresses at diagnosis, and vital status of pediatric CNS tumor cases (n = 5,477) for the period 1995 to 2017 were obtained from the Texas Cancer Registry. ADI scores were computed for census tracts in Texas using the U.S. Census Bureau 2010 geography. Tracts were classified into quartiles as least, third-most, second-most, and most disadvantaged. Children were mapped to quartiles based on residency at diagnosis. The adjusted hazard ratio (HR) and 95% confidence interval (CI) were calculated.

RESULTS

The results showed a significantly increased HR for death among children in the most (HR, 1.29; 95% CI, 1.09-1.51), second-most (HR, 1.18; 95% CI, 1.01-1.38), and third-most disadvantaged census tracts (HR, 1.18; 95% CI, 1.02-1.37) compared with children in the least disadvantaged tracts.

CONCLUSIONS

Children living in the most disadvantaged neighborhoods experienced a significantly higher risk of mortality, indicating the important role of socioeconomic disparities in the survival of pediatric CNS tumors.

IMPACT

The demographic and socioeconomic disparities identified by this study should be considered when planning treatment strategies for these susceptible groups and thus, lead to a better outcome in socioeconomically disadvantaged children diagnosed with CNS tumors.

The role of sex chromosomes and sex hormones in vocal learning systems

Vocal learning is the ability to imitate and modify sounds through auditory experience, a rare trait found in only a few lineages of mammals and birds. It is a critical component of human spoken language, allowing us to verbally transmit speech repertoires and knowledge across generations. In many vocal learning species, the vocal learning trait is sexually dimorphic, where it is either limited to males or present in both sexes to different degrees. In humans, recent findings have revealed subtle sexual dimorphism in vocal learning/spoken language brain regions and some associated disorders. For songbirds, where the neural mechanisms of vocal learning have been well studied, vocal learning appears to have been present in both sexes at the origin of the lineage and was then independently lost in females of some subsequent lineages. This loss is associated with an interplay between sex chromosomes and sex steroid hormones. Even in species with little dimorphism, like humans, sex chromosomes and hormones still have some influence on learned vocalizations. Here we present a brief synthesis of these studies, in the context of sex determination broadly, and identify areas of needed investigation to further understand how sex chromosomes and sex steroid hormones help establish sexually dimorphic neural structures for vocal learning.

The Prenatal Hormone Milieu in Autism Spectrum Disorder

Though the etiology of autism spectrum disorder (ASD) remains largely unknown, recent findings suggest that hormone dysregulation within the prenatal environment, in conjunction with genetic factors, may alter fetal neurodevelopment. Early emphasis has been placed on the potential role of in utero exposure to androgens, particularly testosterone, to theorize ASD as the manifestation of an "extreme male brain." The relationship between autism risk and obstetric conditions associated with inflammation and steroid dysregulation merits a much broader understanding of the in utero steroid environment and its potential influence on fetal neuroendocrine development. The exploration of hormone dysregulation in the prenatal environment and ASD development builds upon prior research publishing associations with obstetric conditions and ASD risk. The insight gained may be applied to the development of chronic adult metabolic diseases that share prenatal risk factors with ASD. Future research directions will also be discussed.

Prenatal smoke exposure induces persistent Cyp2a5 methylation and increases nicotine metabolism in the liver of neonatal and adult male offspring

Prenatal smoke exposure (PSE) is a risk factor for nicotine dependence. One susceptibility gene for nicotine dependence is Cytochrome P450 (CYP) 2A6, an enzyme responsible for the conversion of nicotine to cotinine and nicotine clearance in the liver. Higher activity of the CYP2A6 enzyme is associated with nicotine dependence, but no research has addressed the PSE effects on the CYP2A6 gene or its mouse homologue Cyp2a5. We hypothesized that PSE affects Cyp2a5 promoter methylation, Cyp2a5 mRNA levels, and nicotine metabolism in offspring. We used a smoke-exposed pregnant mouse model. RNA, DNA, and microsomal protein were isolated from liver tissue of foetal, neonatal, and adult offspring. Enzyme activity, Cyp2a5 mRNA levels, and Cyp2a5 methylation status of six CpG sites within the promoter region were analysed via HPLC, RT-PCR, and bisulphite pyrosequencing. Our data show that PSE induced higher cotinine levels in livers of male neonatal and adult offspring compared to controls. PSE-induced cotinine levels in neonates correlated with Cyp2a5 mRNA expression and promoter methylation at CpG-7 and CpG+45. PSE increased methylation in almost all CpG sites in foetal offspring, and this effect persisted at CpG-74 in male neonatal and adult offspring. Our results indicate that male offspring of mothers which were exposed to cigarette smoke during pregnancy have a higher hepatic nicotine metabolism, which could be regulated by DNA methylation. Given the detected persistence into adulthood, extrapolation to the human situation suggests that sons born from smoking mothers could be more susceptible to nicotine dependence later in life.

Neuroprotective and neurotoxic outcomes of androgens and estrogens in an oxidative stress environment

BACKGROUND

The role of sex hormones on cellular function is unclear. Studies show androgens and estrogens are protective in the CNS, whereas other studies found no effects or damaging effects. Furthermore, sex differences have been observed in multiple oxidative stress-associated CNS disorders, such as Alzheimer's disease, depression, and Parkinson's disease. The goal of this study is to examine the relationship between sex hormones (i.e., androgens and estrogens) and oxidative stress on cell viability.

METHODS

N27 and PC12 neuronal and C6 glial phenotypic cell lines were used. N27 cells are female rat derived, whereas PC12 cells and C6 cells are male rat derived. These cells express estrogen receptors and the membrane-associated androgen receptor variant, AR45, but not the full-length androgen receptor. N27, PC12, and C6 cells were exposed to sex hormones either before or after an oxidative stressor to examine neuroprotective and neurotoxic properties, respectively. Estrogen receptor and androgen receptor inhibitors were used to determine the mechanisms mediating hormone-oxidative stress interactions on cell viability. Since the presence of AR45 in the human brain tissue was unknown, we examined the postmortem brain tissue from men and women for AR45 protein expression.

RESULTS

Neither androgens nor estrogens were protective against subsequent oxidative stress insults in glial cells. However, these hormones exhibited neuroprotective properties in neuronal N27 and PC12 cells via the estrogen receptor. Interestingly, a window of opportunity exists for sex hormone neuroprotection, wherein temporary hormone deprivation blocked neuroprotection by sex hormones. However, if sex hormones are applied following an oxidative stressor, they exacerbated oxidative stress-induced cell loss in neuronal and glial cells.

CONCLUSIONS

Sex hormone action on cell viability is dependent on the cellular environment. In healthy neuronal cells, sex hormones are protective against oxidative stress insults via the estrogen receptor, regardless of sex chromosome complement (XX, XY). However, in unhealthy (e.g., high oxidative stress) cells, sex hormones exacerbated oxidative stress-induced cell loss, regardless of cell type or sex chromosome complement. The non-genomic AR45 receptor, which is present in humans, mediated androgen's damaging effects, but it is unknown which receptor mediated estrogen's damaging effects. These differential effects of sex hormones that are dependent on the cellular environment, receptor profile, and cell type may mediate the observed sex differences in oxidative stress-associated CNS disorders.

Hormone-epigenome interactions in behavioural regulation

Interactions between hormones and epigenetic factors are key regulators of behaviour, but the mechanisms that underlie their effects are complex. Epigenetic factors can modify sensitivity to hormones by altering hormone receptor expression, and hormones can regulate epigenetic factors by recruiting epigenetic regulators to DNA. The bidirectional nature of this relationship is becoming increasingly evident and suggests that the ability of hormones to regulate certain forms of behaviour may depend on their ability to induce changes in the epigenome. Moreover, sex differences have been reported for several epigenetic modifications, and epigenetic factors are thought to regulate sexual differentiation of behaviour, although specific mechanisms remain to be understood. Indeed, hormone-epigenome interactions are highly complex and involve both canonical and non-canonical regulatory pathways that may permit for highly specific gene regulation to promote variable forms of behavioural adaptation.

Progesterone receptor-mediated actions and the treatment of central nervous system disorders: An up-date of the known and the challenge of the unknown

Progesterone has been shown to exert a wide range of remarkable protective actions in experimental models of central nervous system injury or disease. However, the intimate mechanisms involved in each of these beneficial effects are not fully depicted. In this review, we intend to give the readers a thorough revision on what is known about the participation of diverse receptors and signaling pathways in progesterone-mediated neuroprotective, pro-myelinating and anti-inflammatory outcomes, as well as point out to novel regulatory mechanisms that could open new perspectives in steroid-based therapies.

The biological basis of sexual orientation: How hormonal, genetic, and environmental factors influence to whom we are sexually attracted

Humans develop relatively stable attractions to sexual partners during maturation and present a spectrum of sexual orientation from homosexuality to heterosexuality encompassing varying degrees of bisexuality, with some individuals also displaying asexuality. Sexual orientation represents a basic life phenomenon for humans. However, the molecular mechanisms underlying these diverse traits of sexual orientation remain highly controversial. In this review, we systematically discuss recent advancements in sexual orientation research, including those related to measurements and associated brain regions. Current findings regarding sexual orientation modulation by hormonal, genetic, maternal immune system, and environmental factors are summarized in both human and model systems. We also emphasize that future studies should recognize the differences between males and females and pay more attention to minor traits and the epigenetic regulation of sexual orientation. A comprehensive view of sexual orientation may promote our understanding of the biological basis of sex, and that of human reproduction, and evolution.

Endocrine-disrupting chemicals: Effects on neuroendocrine systems and the neurobiology of social behavior

A contribution to SBN/ICN special issue. Endocrine-disrupting chemicals (EDCs) are pervasive in the environment. They are found in plastics and plasticizers (bisphenol A (BPA) and phthalates), in industrial chemicals such as polychlorinated biphenyls (PCBs), and include some pesticides and fungicides such as vinclozolin. These chemicals act on hormone receptors and their downstream signaling pathways, and can interfere with hormone synthesis, metabolism, and actions. Because the developing brain is particularly sensitive to endogenous hormones, disruptions by EDCs can change neural circuits that form during periods of brain organization. Here, we review the evidence that EDCs affect developing hypothalamic neuroendocrine systems, and change behavioral outcomes in juvenile, adolescent, and adult life in exposed individuals, and even in their descendants. Our focus is on social, communicative and sociosexual behaviors, as how an individual behaves with a same- or opposite-sex conspecific determines that individual's ability to exist in a community, be selected as a mate, and reproduce successfully.

Sex-Specific Regulation of Fear Memory by Targeted Epigenetic Editing of Cdk5

BACKGROUND

Sex differences in the expression and prevalence of trauma- and stress-related disorders have led to a growing interest in the sex-specific molecular and epigenetic mechanisms underlying these diseases. Cyclin-dependent kinase 5 (CDK5) is known to underlie both fear memory and stress behavior in male mice. Given our recent finding that targeted histone acetylation of Cdk5 regulates stress responsivity in male mice, we hypothesized that such a mechanism may be functionally relevant in female mice as well.

METHODS

We applied epigenetic editing of Cdk5 in the hippocampus and examined the regulation of fear memory retrieval in male and female mice. Viral expression of zinc finger proteins targeting histone acetylation to the Cdk5 promoter was paired with a quantification of learning and memory of contextual fear conditioning, expression of CDK5, and enrichment of histone modifications of the Cdk5 gene.

RESULTS

We found that male mice exhibit stronger long-term memory retrieval than do female mice, and this finding was associated with male-specific epigenetic activation of hippocampal Cdk5 expression. Sex differences in behavior and epigenetic regulation of Cdk5 occurred after long-term, but not short-term, fear memory retrieval. Finally, targeted histone acetylation of hippocampal Cdk5 promoter attenuated fear memory retrieval and increased tau phosphorylation in female but not male mice.

CONCLUSIONS

Epigenetic editing uncovered a female-specific role of Cdk5 activation in attenuating fear memory retrieval. This finding may be attributed to CDK5 mediated hyperphosphorylation of tau only in the female hippocampus. Sex-specific epigenetic regulation of Cdk5 may reflect differences in the effect of CDK5 on downstream target proteins that regulate memory.

Sex-Dependent Effects of 2,2',3,5',6-Pentachlorobiphenyl on Dendritic Arborization of Primary Mouse Neurons

Early life exposures to environmental contaminants are implicated in the pathogenesis of many neurodevelopmental disorders (NDDs). These disorders often display sex biases, but whether environmental neurotoxicants act in a sex-dependent manner to modify neurodevelopment is largely unknown. Since altered dendritic morphology is associated with many NDDs, we tested the hypothesis that male and female primary mouse neurons are differentially susceptible to the dendrite-promoting activity of 2,2',3,5',6-pentachlorobiphenyl (PCB 95). Hippocampal and cortical neuron-glia co-cultures were exposed to vehicle (0.1% dimethylsulfoxide) or PCB 95 (100 fM-1 μM) from day in vitro 7-9. As determined by Sholl analysis, PCB 95-enhanced dendritic growth in female but not male hippocampal and cortical neurons. In contrast, both male and female neurons responded to bicuculline with increased dendritic complexity. Detailed morphometric analyses confirmed that PCB 95 effects on the number and length of primary and nonprimary dendrites varied depending on sex, brain region and PCB concentration, and that female neurons responded more consistently with increased dendritic growth and at lower concentrations of PCB 95 than their male counterparts. Exposure to PCB 95 did not alter cell viability or the ratio of neurons to glia in cultures of either sex. These results demonstrate that cultured female mouse hippocampal and cortical neurons are more sensitive than male neurons to the dendrite-promoting activity of PCB 95, and suggest that mechanisms underlying PCB 95-induced dendritic growth are sex-dependent. These data highlight the importance of sex in neuronal responses to environmental neurotoxicants.

Passing experiences on to future generations: endocrine disruptors and transgenerational inheritance of epimutations in brain and sperm

All animals have body burdens of polychlorinated biphenyls (PCBs) despite their ban decades ago. These and modern endocrine-disrupting chemicals (EDCs) such as the fungicide vinclozolin (VIN) perturb hormone signaling and lead to dysfunctions following prenatal exposures. Beyond direct exposures, transgenerational disease phenotypes can persist for multiple generations without subsequent exposure. The mechanisms of action of these EDCs differ: VIN is anti-androgenic while the PCB mixture Aroclor 1221 (A1221) is weakly estrogenic. Based on limited evidence for the inheritance of epimutations in germline, we measured DNA methylation in brain and sperm of rats. Pregnant dams were exposed from day 8-18 of gestation to low dosages of VIN, A1221, or the vehicle. To produce paternal lineages, exposed F1 males were bred with untreated females, creating the F2 and subsequently F3 generations. In adult F1 and F3 males, mature sperm was collected, and brain nuclei involved in anxiety and social behaviors (CA3 of the hippocampus; central amygdala) were selected for assays of epimutations in CpG islands using reduced representation bisulfite sequencing. In F1 sperm, VIN and PCBs induced differential methylation in 215 and 284 CpG islands, respectively, compared to vehicle. The majority of effects were associated with hypermethylation. Fewer epimutations were detected in the brain. A subset of differentially methylated regions were retained from the F1 to the F3 generation, suggesting a common mechanism of EDC and germline epigenome interaction. Thus, EDCs can cause heritable epimutations in the sperm that may embody the future phenotype of brain-behavior disorders caused by direct or transgenerational exposures.

Genome-wide methylation study of whole blood cells DNA in men with congenital hypopituitarism disease

Congenital hypopituitarism (CH) is a relatively rare disease that is characterized by the deficiency of one or more hormones secreted by the pituitary gland, which leads to metabolic disorders, amenorrhea and infertility. However, the underlying molecular mechanisms of CH have not yet been fully elucidated. The present study evaluated the genome-wide methylation level of whole blood DNA in 12 patients with CH and 12 age-matched controls using Illumina Human Methylation 450 array, in order to determine the roles of epigenetic regulation in the pathogenesis of CH. The results demonstrated that the methylation levels of 51 CpG sites were significantly different between the patients with CH and the controls. Functional enrichment analysis identified that the aberrant methylated genes were enriched in gene sets associated with metabolic or cellular process, immune system process and reproduction. In addition, two CpG sites on genes LIM domain kinase 2 (LIMK2) and piwi-like RNA-mediated gene silencing 2 (PIWIL2), which are involved in spermatogenesis and/or testicular development, were identified to be hypermethylated in male patients with CH. The hypermethylation of these sites was further validated in another 40 patients with CH and 40 matched controls with a quantitative bisulfite pyrosequencing method, and the methylation levels of these two loci demonstrated promising diagnostic capacities for CH. The present results suggested that aberrant methylation of genes may be involved in the pathogenesis of CH, and hypermethylation of LIMK2 and PIWIL2 may contribute to the infertility of male patients with CH. Further studies are required to elucidate the underlying mechanisms of the epigenetic regulation of these genes.

Is Sexual Differentiation of Brain and Behavior Epigenetic?

Sexual differentiation of brain and behavior is largely a hormonally driven process occurring perinatally in rodents and prenatally in primates. Considered early life programming, this process occurs at a time when the brain is remarkably immature and often does not manifest until reproductive maturity, raising the question of how brief hormonal exposure early in life could have such an enduring effect. Epigenetic modifications that occur early and persist into adulthood is one feasible explanation. Sufficient evidence exists to confirm that there are indeed epigenetic changes to specific brain regions induced by steroid hormones in males to differentiate them from females, but whether they persist into adulthood is unclear. Regardless, there are strong correlations between early epigenetic changes and adult brain and behavior. Moreover, although generally referred to as a permanent process, there is evidence that adult sex-typic behaviors are malleable and even reversible in mammals under certain conditions and these may be a function of epigenetic maintenance of gene expression that impacts behavior.

Methamphetamine alters DNMT and HDAC activity in the posterior dorsal medial amygdala in an ovarian steroid-dependent manner

Methamphetamine (Meth) is a psychomotor stimulant associated with increased sexual drive and risky sexual behaviors in both men and women. Females are comparatively understudied, despite the fact that are just as likely as men to use methamphetamine. Importantly, Meth-associated sexual behaviors put female-users at a greater risk for unplanned pregnancies, and increase the risk of psychiatric co-morbidities such as depression. Our work in a rodent model has demonstrated that in the presence of the ovarian steroids, estradiol (EB) and progesterone (P), methamphetamine facilitates the activation of neurons of in the Medial Amygdala (MePD) and Ventromedial Nucleus of the Hypothalamus (VMN), nuclei that are integral to female sexual behavior. As methamphetamine has been previously associated with epigenetic changes in males, we hypothesized that methamphetamine may facilitate sexual motivation in females by modulating the amount of epigenetic enzymatic activity in the VMN and MePD. To test this hypothesis, histone deacetylase (HDAC) and DNA methyltransferase (DNMT) activity was quantitated in both the VMN and MePD in the presence and absence of methamphetamine in femalerats who were ovariectomized (OVX), or OVXed and hormone replaced with EB + P. DMNT1 and DNMT3B protein levels were also assessed. Our results show that methamphetamine alters DNMT and HDAC activity in the MePD in an ovarian steroid-dependent fashion. Both methamphetamine alone and EB + P alone significantly reduce DNMT enzymatic activity in an OVX female, but do not further decrease activity when both are given in combination. In contrast, no changes in HDAC or DNMT activity were seen in the VMN regardless of treatment, but the amount of DNMT3b after methamphetamine was significantly altered depending on the presence or absence of ovarian steroids. Taken together, these results support the hypothesis that methamphetamine induces change on an epigenetic level in female rats in both a hormone and nucleus dependent manner, and suggests epigenetic changes may play a role in methamphetamine's mechanism to facilitate the sexual motivation.

Neuroactive steroids, neurosteroidogenesis and sex

The nervous system is a target and a source of steroids. Neuroactive steroids are steroids that target neurons and glial cells. They include hormonal steroids originated in the peripheral glands, steroids locally synthesized by the neurons and glial cells (neurosteroids) and synthetic steroids, some of them used in clinical practice. Here we review the mechanisms of synthesis, metabolism and action of neuroactive steroids, including the role of epigenetic modifications and the mitochondria in their sex specific actions. We examine sex differences in neuroactive steroid levels under physiological conditions and their role in the establishment of sex dimorphic structures in the nervous system and sex differences in its function. In addition, particular attention is paid to neuroactive steroids under pathological conditions, analyzing how pathology alters their levels and their role as neuroprotective factors, considering the influence of sex in both cases.

Mechanisms of Sex Differences in Fear and Posttraumatic Stress Disorder

Following sexual maturity, females disproportionately have higher rates of posttraumatic stress disorder (PTSD) and experience greater symptom severity and chronicity as compared with males. This observation has led many to examine sex differences in PTSD risk factors. Though relatively few, these studies reveal that the root causes of PTSD sex differences are complex, and partly represent interactions between sex-specific nonbiological and biological risk factors, which differentially shape PTSD vulnerability. Moreover, these studies suggest that sex-specific PTSD vulnerability is partly regulated by sex differences in fear systems. Fear, which represents a highly conserved adaptive response to threatening environmental stimuli, becomes pathological in trauma- and stress-based psychiatric syndromes, such as PTSD. Over the last 30 years, considerable progress has been made in understanding normal and pathological molecular and behavioral fear processes in humans and animal models. Thus, fear mechanisms represent a tractable PTSD biomarker in the study of sex differences in fear. In this review, we discuss studies that examine nonbiological and biological sex differences that contribute to normal and pathological fear behaviors in humans and animal models. This, we hope, will shed greater light on the potential mechanisms that contribute to increased PTSD vulnerability in females.

Epigenetic Landscapes of the Adversity-Exposed Brain

It is understood that adversity during development has the power to alter behavioral trajectories, and the role of the epigenome in that relationship is currently under intense investigation. Several studies in both nonhuman animals and humans have established a link between early adversity and epigenetic regulation of genes heavily implicated in the stress response, plasticity and cognition, and psychiatric disorders such as depression and anxiety. Thus the relatively recent surge of studies centering on the epigenetic outcomes of stress has great potential to inform treatments and interventions for psychiatric disorder precipitated by early adversity. Here we review what we know and what we do not know, and suggest approaches to help further elucidate the relationship between early adversity, epigenetics, and behavior.

Species and Sex Differences in the Morphogenic Response of Primary Rodent Neurons to 3,3'-Dichlorobiphenyl (PCB 11)

PCB 11 is an emerging global pollutant that we recently showed promotes axonal and dendritic growth in primary rat neuronal cell cultures. Here, we address the influence of sex and species on neuronal responses to PCB 11. Neuronal morphology was quantified in sex-specific primary hippocampal and cortical neuron-glia co-cultures derived from neonatal C57BL/6J mice and Sprague Dawley rats exposed for 48 h to vehicle (0.1% DMSO) or PCB 11 at concentrations ranging from 1 fM to 1 nM. Total axonal length was quantified in tau-1 immunoreactive neurons at day in vitro (DIV) 2; dendritic arborization was assessed by Sholl analysis at DIV 9 in neurons transfected with MAP2B-FusRed. In mouse cultures, PCB 11 enhanced dendritic arborization in female, but not male, hippocampal neurons and male, but not female, cortical neurons. In rat cultures, PCB 11 promoted dendritic arborization in male and female hippocampal and cortical neurons. PCB 11 also increased axonal growth in mouse and rat neurons of both sexes and neuronal cell types. These data demonstrate that PCB 11 exerts sex-specific effects on neuronal morphogenesis that vary depending on species, neurite type, and neuronal cell type. These findings have significant implications for risk assessment of this emerging developmental neurotoxicant.

Genetic and epigenetic factors underlying sex differences in the regulation of gene expression in the brain

There are inherent biological differences between males and females that contribute to sex differences in brain function and to many sex-specific illnesses and disorders. Traditionally, it has been thought that such differences are due largely to hormonal regulation; however, there are also genetic and epigenetic effects caused by the inheritance and unequal dosage of genes located on the X and Y chromosomes. Here we discuss the evidence in favor of a genetic and epigenetic basis for sexually dimorphic behavior, as a consequence of underlying differences in the regulation of genes that drive brain function. A better understanding of sex-specific molecular processes in the brain will provide further insight for the development of novel therapeutic approaches for the treatment of neuropsychiatric disorders characterized by sex differences. © 2016 Wiley Periodicals, Inc.

Effects of perinatal bisphenol A exposure on the volume of sexually-dimorphic nuclei of juvenile rats: A CLARITY-BPA consortium study

Bisphenol A (BPA) is a high volume endocrine disrupting chemical found in a wide variety of products including plastics and epoxy resins. Human exposure is nearly ubiquitous, and higher in children than adults. Because BPA has been reported to interfere with sex steroid hormone signaling, there is concern that developmental exposure, even at levels below the current FDA No Observed Adverse Effect Level (NOAEL) of 5mg/kg body weight (bw)/day, can disrupt brain sexual differentiation. The current studies were conducted as part of the CLARITY-BPA (Consortium Linking Academic and Regulatory Insights on BPA Toxicity) program and tested the hypothesis that perinatal BPA exposure would induce morphological changes in hormone sensitive, sexually dimorphic brain regions. Sprague-Dawley rats were randomly assigned to 5 groups: BPA (2.5, 25, or 2500μg/kgbw/day), a reference estrogen (0.5μg ethinylestradiol (EE₂)/kgbw/day), or vehicle. Exposure occurred by gavage to the dam from gestational day 6 until parturition, and then to the offspring from birth through weaning. Unbiased stereology was used to quantify the volume of the sexually dimorphic nucleus (SDN), the anteroventral periventricular nucleus (AVPV), the posterodorsal portion of the medial amygdala (MePD), and the locus coeruleus (LC) at postnatal day 28. No appreciable effects of BPA were observed on the volume of the SDN or LC. However, AVPV volume was enlarged in both sexes, even at levels below the FDA NOAEL. Collectively, these data suggest the developing brain is vulnerable to endocrine disruption by BPA at exposure levels below previous estimates by regulatory agencies.

In vivo and in vitro sex differences in the dendritic morphology of developing murine hippocampal and cortical neurons

Altered dendritic morphology is common in neurodevelopmental disorders (NDDs), many of which show sex biases in prevalence, onset and/or severity. However, whether dendritic morphology varies as a function of sex in juvenile mice or primary neuronal cell cultures is largely unknown even though both are widely used models for studying NDDs. To address this gap, we quantified dendritic morphology in CA1 pyramidal hippocampal and adjacent somatosensory pyramidal cortical neurons from male and female postnatal day (P)28 C57BL/6J mice. As determined by Sholl analysis of Golgi-stained brain sections, dendritic arbors of male hippocampal neurons are more complex than females. Conversely, dendritic morphology of female cortical neurons is more complex than males. In primary neuron-glia co-cultures from P0 mouse hippocampi, male neurons have more complex dendritic arbors than female neurons. Sex differences are less pronounced in cortical cultures. In vitro sex differences in dendritic morphology are driven in part by estrogen-dependent mechanisms, as evidenced by decreased dendritic complexity in male hippocampal neurons cultured in phenol red-free media or in the presence of an estrogen receptor antagonist. Evidence that sex influences dendritic morphogenesis in two models of neurodevelopment in a region-specific manner has significant mechanistic implications regarding sex biases in NDDs.

Neuroimmunology and neuroepigenetics in the establishment of sex differences in the brain

The study of sex differences in the brain is a topic of neuroscientific study that has broad reaching implications for culture, society and biomedical science. Recent research in rodent models has led to dramatic shifts in our views of the mechanisms underlying the sexual differentiation of the brain. These include the surprising discoveries of a role for immune cells and inflammatory mediators in brain masculinization and a role for epigenetic suppression in brain feminization. How and to what degree these findings will translate to human brain development will be questions of central importance in future research in this field.

Epigenetic impacts of endocrine disruptors in the brain

The acquisition of reproductive competence is organized and activated by steroid hormones acting upon the hypothalamus during critical windows of development. This review describes the potential role of epigenetic processes, particularly DNA methylation, in the regulation of sexual differentiation of the hypothalamus by hormones. We examine disruption of these processes by endocrine-disrupting chemicals (EDCs) in an age-, sex-, and region-specific manner, focusing on how perinatal EDCs act through epigenetic mechanisms to reprogram DNA methylation and sex steroid hormone receptor expression throughout life. These receptors are necessary for brain sexual differentiation and their altered expression may underlie disrupted reproductive physiology and behavior. Finally, we review the literature on histone modifications and non-coding RNA involvement in brain sexual differentiation and their perturbation by EDCs. By putting these data into a sex and developmental context we conclude that perinatal EDC exposure alters the developmental trajectory of reproductive neuroendocrine systems in a sex-specific manner.

Cooperation of Genomic and Rapid Nongenomic Actions of Estrogens in Synaptic Plasticity

Neuroplasticity refers to the changes in the molecular and cellular processes of neural circuits that occur in response to environmental experiences. Clinical and experimental studies have increasingly shown that estrogens participate in the neuroplasticity involved in cognition, behavior, and memory. It is generally accepted that estrogens exert their effects through genomic actions that occur over a period of hours to days. However, emerging evidence indicates that estrogens also rapidly influence the neural circuitry through nongenomic actions. In this review, we provide an overview of the genomic and nongenomic actions of estrogens and discuss how these actions may cooperate in synaptic plasticity. We then summarize the role of epigenetic modifications, synaptic protein synthesis, and posttranslational modifications, and the splice variants of estrogen receptors in the complicated network of estrogens. The combination of genomic and nongenomic mechanisms endows estrogens with considerable diversity in modulating neural functions including synaptic plasticity.

Estrogen in prefrontal cortex blocks stress-induced cognitive impairments in female rats

Animal and human studies have found that males and females show distinct stress responses. Recent studies suggest the contribution of estrogen in the brain to this sexual dimorphism. Repeated stress has been found to impair cognitive behaviors via suppressing glutamatergic transmission and glutamate receptor surface expression in pyramidal neurons of prefrontal cortex (PFC) in male rats. On the contrary, female rats exposed to the same stress paradigms show normal synaptic function and PFC-mediated cognition. The level of aromatase, the enzyme for the biosynthesis of estrogen, is significantly higher in the PFC of females than males. The stress-induced glutamatergic deficits and memory impairment are unmasked by blocking estrogen receptors or aromatase in females, suggesting a protective role of estrogen against the detrimental effects of repeated stress.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Neonatal exposure to 17β-estradiol down-regulates the expression of synaptogenesis related genes in selected brain regions of adult female rats

AIMS

Administration of estradiol or compounds with estrogenic activity to newborn female rats results in irreversible masculinization as well as defeminization in the brain and the animals exhibit altered reproductive behavior as adults. The cellular and molecular mechanism involved in inducing the irreversible changes is largely unknown. In the present study, we have monitored the changes in the expression of selected synaptogenesis related genes in the sexually dimorphic brain regions such as POA, hypothalamus and pituitary following 17β-estradiol administration to neonatal female rats.

MAIN METHODS

Female Wistar rats which were administered 17β-estradiol on day 2 and 3 after birth were sacrificed 120days later and the expression levels of genes implicated in synaptogenesis were monitored by semi-quantitative reverse transcription PCR. Since estradiol induced up-regulation of COX-2 in POA is a marker for estradiol induced masculinization as well as defeminization, in the present study only animals in which the increase in expression of COX-2 gene was observed in POA were included in the study.

KEY FINDINGS

Down-regulation of genes such as NMDA-2B, NETRIN-1, BDNF, MT-5 MMP and TNF-α was observed in the pre-optic area of neonatally E2 treated female rat brain but not in hypothalamus and pituitary compared to the vehicle- treated controls as assessed by RT-PCR and Western blot analysis.

SIGNIFICANCE

Our results suggest a possibility that down-regulation of genes associated with synaptogenesis in POA, may be resulting in disruption of the cyclical regulation of hormone secretion by pituitary the consequence of which could be infertility and altered reproductive behavior.

Transgenerational effects of 17α-ethinyl estradiol on anxiety behavior in the guppy, Poecilia reticulata

Environmental contaminants can cause alterations that can be transgenerationally transmitted to subsequent generations. Estrogens are among those contaminants shown to induce heritable changes that persist over generations in mammals. Results in other vertebrates are few. We have analyzed the effects on anxiety of 17α-ethinyl estradiol (EE2) in the F1 and F2 generations in guppies, Poecilia reticulata, obtained from F0 fish maternally exposed to 0 or 20ng/L EE2 until birth. F0 males and females were bred with fish of the same treatment but different families producing F1 offspring. Behavior in the novel tank test at 6months revealed that males with EE2-exposed parents had significantly longer latency to the upper half of the tank than control males, while no EE2 effects were observed in females. Also in F2, obtained from F1 as above, males in the EE2 group had longer latency time compared to control males, with no differences due to EE2-exposure of F0 observed in females. In the scototaxis (light/dark preference) test, latency to first transition to black compartment and total transitions to black were significantly altered in females due to EE2 exposure of F0 while the total time in black was higher in males with EE2-exposed F0 compared with controls. The increased anxiety in the F2 generation demonstrates a transgenerational anxiety phenotype and shows that non-reproductive behavior can be transgenerationally modified by estrogens in fish.

Are females more variable than males in gene expression? Meta-analysis of microarray datasets

Background

The majority of preclinical biomedical research involves studies of males rather than females. It is thought that researchers have avoided females based on the idea that female traits are more variable than those of males because of cyclic variation in effects of ovarian hormones.

Methods

To test the assumption of inherently greater female variability, we analyzed 293 microarray datasets measuring gene expression in various tissues of mice and humans, comprising analysis of more than 5 million probes.

Results

Meta-analysis showed that on average, male gene expression is slightly more variable than that of females although the difference is small. We also tested if the X chromosome of humans shows greater variability in gene expression in males than in females, as might be expected because of hemizygous exposure of polymorphic X alleles but again found little sex difference.

Conclusion

Our analysis supports and extends previous studies reporting no overall greater phenotypic variability in females.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-015-0036-8) contains supplementary material, which is available to authorized users.

At the frontier of epigenetics of brain sex differences

The notion that epigenetics may play an important role in the establishment and maintenance of sex differences in the brain has garnered great enthusiasm but the reality in terms of actual advances has been slow. Two general approaches include the comparison of a particular epigenetic mark in males vs. females and the inhibition of key epigenetic enzymes or co-factors to determine if this eliminates a particular sex difference in brain or behavior. The majority of emphasis has been on candidate genes such as steroid receptors. Only recently have more generalized survey type approaches been achieved and these promise to open new vistas and accelerate discovery of important roles for DNA methylation, histone modification, genomic imprinting and microRNAs (miRs). Technical challenges abound and, while not unique to this field, will require novel thinking and new approaches by behavioral neuroendocrinologists.

Developmental exposure of zebrafish (Danio rerio) to 17α-ethinylestradiol affects non-reproductive behavior and fertility as adults, and increases anxiety in unexposed progeny

Exposure to estrogenic endocrine disruptors (EDCs) during development affects fertility, reproductive and non-reproductive behavior in mammals and fish. These effects can also be transferred to coming generations. In fish, the effects of developmental EDC exposure on non-reproductive behavior are less well studied. Here, we analyze the effects of 17α-ethinylestradiol (EE2) on anxiety, shoaling behavior and fertility in zebrafish after developmental treatment and remediation in clean water until adulthood. Zebrafish embryos were exposed from day 1 to day 80 post fertilization to actual concentrations of 1.2 and 1.6ng/L EE2. After remediation for 82days non-reproductive behavior and fertilization success were analyzed in both sexes. Males and females from the 1.2ng/L group, as well as control males and females, were bred, and behavior of the untreated F1 offspring was tested as adults. Developmental treatment with 1.2 and 1.6ng/L EE2 significantly increased anxiety in the novel tank test and increased shoaling intensity in both sexes. Fertilization success was significantly reduced by EE2 in both sexes when mated with untreated fish of opposite sex. Progeny of fish treated with 1.2ng/L EE2 showed increased anxiety in the novel tank test and increased light avoidance in the scototaxis test compared to control offspring. In conclusion, developmental exposure of zebrafish to low doses of EE2 resulted in persistent changes in behavior and fertility. The behavior of unexposed progeny was affected by their parents' exposure, which might suggest transgenerational effects.

The Neurobiology and Psychology of Pedophilia: Recent Advances and Challenges

A pedophilic disorder is recognized for its impairment to the individual and for the harm it may cause to others. Pedophilia is often considered a side issue and research into the nature of pedophilia is delayed in comparison to research into other psychiatric disorders. However, with the increasing use of neuroimaging techniques, such as functional and structural magnetic resonance imaging (sMRI, fMRI), together with neuropsychological studies, we are increasing our knowledge of predisposing and accompanying factors contributing to pedophilia development. At the same time, we are faced with methodological challenges, such as group differences between studies, including age, intelligence, and comorbidities, together with a lack of careful assessment and control of child sexual abuse. Having this in mind, this review highlights the most important studies investigating pedophilia, with a strong emphasis on (neuro-) biological studies, combined with a brief explanation of research into normal human sexuality. We focus on some of the recent theories on the etiology of pedophilia such as the concept of a general neurodevelopmental disorder and/or alterations of structure and function in frontal, temporal, and limbic brain areas. With this approach, we aim to not only provide an update and overview but also a framework for future research and to address one of the most significant questions of how pedophilia may be explained by neurobiological and developmental alterations.

Epigenetic modifications of gene promoter DNA in the liver of adult female mice masculinized by testosterone

Testosterone (T) is known to masculinize the female phenotype of the liver, evidenced as up- and down-regulated expressions of male- and female-predominant genes, respectively, involved in hepatic metabolism. This study is aimed at identifying epigenetic modifications of promoters of these differently expressed genes in the liver after masculinization by T of adult female C57BL/6 mice using methylated DNA immunoprecipitation and NimbleGen microarrays. Among the 17,354 promoters examined, 82 promoters in the liver have been identified to be significantly changed by T (p<0.05), with 47 and 35 promoters exhibiting increased and decreased DNA methylation, respectively. Most of these promoters display the changes of DNA methylation in their Ups-regions, which are between +500 and +2000 bp upstream from the transcription start site (TSS) of the genes. Less T-induced modifications have been detected in the Cor-regions of the promoters, i.e., +500 to -500 bp around the TSS. Only 13 and 7 Cor-promoters are hyper- and hypo-methylated, respectively, among which are 10 hyper- and 5 hypo-methylated promoters of genes with annotated functions. Surprisingly, the promoters are largely unmethylated in those genes whose expression has been previously found to be permanently deregulated by T in the liver, as e.g. the T-upregulated male-predominant genes Cyp7b1, Cyp2d9, Cyp4a10, Ugt2b1, Ugt2b38, Hsd3b5, Slco1a1 as well as the T-downregulated female-predominant genes Cyp2b9, Cyp2b13, Cyp3a41, Cyp3a44, Fmo3, Sult2a2, respectively. Though methylatable, the promoter DNA of Ar, Esr1, and Esr2 remained unaffected by T. However, T decreases DNA-methylation of the Cor-promoter region of Ddc encoding the AR-coactivator dopa decarboxylase. Among the identified 15 Cor-promoters of genes with annotated functions are also those of Defb43, Cst11, and Sele involved in innate immunity. Our data support the view that T may exert long-lasting epigenetic effects on functions of the liver-inherent immune system.

Implications of prenatal steroid perturbations for neurodevelopment, behavior, and autism

The prenatal brain develops under the influence of an ever-changing hormonal milieu that includes endogenous fetal gonadal and adrenal hormones, placental and maternal hormones, and exogenous substances with hormonal activity that can cross the placental barrier. This review discusses the influences of endogenous fetal and maternal hormones on normal brain development and potential consequences of pathophysiological hormonal perturbations to the developing brain, with particular reference to autism. We also consider the effects of hormonal pharmaceuticals used for assisted reproduction, the maintenance of pregnancy, the prevention of congenital adrenal hypertrophy, and hormonal contraceptives continued into an unanticipated pregnancy, among others. These treatments, although in some instances life-saving, may have unintended consequences on the developing fetuses. Additional concern is raised by fetal exposures to endocrine-disrupting chemicals encountered universally by pregnant women from food/water containers, contaminated food, household chemicals, and other sources. What are the potential outcomes of prenatal steroid perturbations on neurodevelopmental and behavioral disorders, including autism-spectrum disorders? Our purposes here are 1) to summarize some consequences of steroid exposures during pregnancy for the development of brain and behavior in the offspring; 2) to summarize what is known about the relationships between exposures and behavior, including autism spectrum disorders; 3) to discuss the molecular underpinnings of such effects, especially molecular epigenetic mechanisms of prenatal steroid manipulations, a field that may explain effects of direct exposures, and even transgenerational effects; and 4) for all of these, to add cautionary notes about their interpretation in the name of scientific rigor.

Sexually dimorphic responses to early adversity: implications for affective problems and autism spectrum disorder

During gestation, development proceeds at a pace that is unmatched by any other stage of the life cycle. For these reasons the human fetus is particularly susceptible not only to organizing influences, but also to pathogenic disorganizing influences. Growing evidence suggests that exposure to prenatal adversity leads to neurological changes that underlie lifetime risks for mental illness. Beginning early in gestation, males and females show differential developmental trajectories and responses to stress. It is likely that sex-dependent organization of neural circuits during the fetal period influences differential vulnerability to mental health problems. We consider in this review evidence that sexually dimorphic responses to early life stress are linked to two developmental disorders: affective problems (greater female prevalence) and autism spectrum disorder (greater male prevalence). Recent prospective studies illustrating the neurodevelopmental consequences of fetal exposure to stress and stress hormones for males and females are considered here. Plausible biological mechanisms including the role of the sexually differentiated placenta are discussed.

Neuroanatomy and sex differences of the lordosis-inhibiting system in the lateral septum

Female sexual behavior in rodents, termed lordosis, is controlled by facilitatory and inhibitory systems in the brain. It has been well demonstrated that a neural pathway from the ventromedial hypothalamic nucleus (VMN) to the midbrain central gray (MCG) is essential for facilitatory regulation of lordosis. The neural pathway from the arcuate nucleus to the VMN, via the medial preoptic nucleus, in female rats mediates transient suppression of lordosis, until female sexual receptivity is induced. In addition to this pathway, other regions are involved in inhibitory regulation of lordosis in female rats. The lordosis-inhibiting systems exist not only in the female brain but also in the male brain. The systems contribute to suppression of heterotypical sexual behavior in male rats, although they have the potential ability to display lordosis. The lateral septum (LS) exerts an inhibitory influence on lordosis in both female and male rats. This review focuses on the neuroanatomy and sex differences of the lordosis-inhibiting system in the LS. The LS functionally and anatomically links to the MCG to exert suppression of lordosis. Neurons of the intermediate part of the LS (LSi) serve as lordosis-inhibiting neurons and project axons to the MCG. The LSi-MCG neural connection is sexually dimorphic, and formation of the male-like LSi-MCG neural connection is affected by aromatized testosterone originating from the testes in the postnatal period. The sexually dimorphic LSi-MCG neural connection may reflect the morphological basis of sex differences in the inhibitory regulation of lordosis in rats.

The effects of perinatal testosterone exposure on the DNA methylome of the mouse brain are late-emerging

Background

The biological basis for sex differences in brain function and disease susceptibility is poorly understood. Examining the role of gonadal hormones in brain sexual differentiation may provide important information about sex differences in neural health and development. Permanent masculinization of brain structure, function, and disease is induced by testosterone prenatally in males, but the possible mediation of these effects by long-term changes in the epigenome is poorly understood.

Methods

We investigated the organizational effects of testosterone on the DNA methylome and transcriptome in two sexually dimorphic forebrain regions—the bed nucleus of the stria terminalis/preoptic area and the striatum. To study the contribution of testosterone to both the establishment and persistence of sex differences in DNA methylation, we performed genome-wide surveys in male, female, and female mice given testosterone on the day of birth. Methylation was assessed during the perinatal window for testosterone's organizational effects and in adulthood.

Results

The short-term effect of testosterone exposure was relatively modest. However, in adult animals the number of genes whose methylation was altered had increased by 20-fold. Furthermore, we found that in adulthood, methylation at a substantial number of sexually dimorphic CpG sites was masculinized in response to neonatal testosterone exposure. Consistent with this, testosterone's effect on gene expression in the striatum was more apparent in adulthood.

Conclusion

Taken together, our data imply that the organizational effects of testosterone on the brain methylome and transcriptome are dramatic and late-emerging. Our findings offer important insights into the long-term molecular effects of early-life hormonal exposure.

Investigation of the effects of subchronic low dose oral exposure to bisphenol A (BPA) and ethinyl estradiol (EE) on estrogen receptor expression in the juvenile and adult female rat hypothalamus

Concerns have been raised regarding the long-term impacts of early life exposure to the ubiquitous environmental contaminant bisphenol A (BPA) on brain organization. Because BPA has been reported to affect estrogen signaling, and steroid hormones play a critical role in brain sexual differentiation, there is also concern that BPA exposure could alter neural sex differences. Here, we examine the impact of subchronic exposure from gestation to adulthood to oral doses of BPA below the current no-observed-adverse-effect level (NOAEL) of 5 mg/kg body weight (bw)/day on estrogen receptor (ESR) expression in sexually dimorphic brain regions of prepubertal and adult female rats. The dams were gavaged daily with vehicle (0.3% carboxymethylcellulose), 2.5, 25, 260, or 2700 μg BPA/kg bw/day, or 0.5 or 5.0 μg ethinyl estradiol (EE)/kg bw/day from gestational day 6 until labor began. Offspring were then gavaged directly from the day after birth until the day before scheduled sacrifice on postnatal days 21 or 90. Using in situ hybridization, one or more BPA doses produced significant decreases in Esr1 expression in the juvenile female rat anteroventral periventricular nucleus (AVPV) of the hypothalamus and significant decreases in Esr2 expression in the adult female rat AVPV and medial preoptic area (MPOA), relative to vehicle controls. BPA did not simply reproduce EE effects, indicating that BPA is not acting solely as an estrogen mimic. The possible consequences of long-term changes in hypothalamic ESR expression resulting from subchronic low dose BPA exposure on neuroendocrine effects are discussed and being addressed in ongoing, related work.

Sex differences in DNA methylation may contribute to risk of PTSD and depression: a review of existing evidence

There are well-established sex differences in the prevalence of certain mental disorders. Work in animal models has provided us with an emerging understanding of the role that epigenetic factors play in establishing sex differences in the brain during development. Similarly, work in animal models, and a more limited but growing literature based on human studies, has demonstrated that DNA methylation (DNAm) changes occur in response to environmental stress, with some of these occurring in a sex-specific manner. In this review, we explore whether DNAm plays a role in contributing to the observed sex differences in prevalence of mental disorders in which stress contributes significantly to their etiologies, specifically posttraumatic stress disorder (PTSD) and depression. We propose that investigating sex differences in DNAm among genes known to influence brain development may help to shed light on the sexually dimorphic risk for, or resilience to, developing PTSD and depression.

Reversible DNA methylation regulates seasonal photoperiodic time measurement

In seasonally breeding vertebrates, changes in day length induce categorically distinct behavioral and reproductive phenotypes via thyroid hormone-dependent mechanisms. Winter photoperiods inhibit reproductive neuroendocrine function but cannot sustain this inhibition beyond 6 mo, ensuring vernal reproductive recrudescence. This genomic plasticity suggests a role for epigenetics in the establishment of seasonal reproductive phenotypes. Here, we report that DNA methylation of the proximal promoter for the type III deiodinase (dio3) gene in the hamster hypothalamus is reversible and critical for photoperiodic time measurement. Short photoperiods and winter-like melatonin inhibited hypothalamic DNA methyltransferase expression and reduced dio3 promoter DNA methylation, which up-regulated dio3 expression and induced gonadal regression. Hypermethylation attenuated reproductive responses to short photoperiods. Vernal refractoriness to short photoperiods reestablished summer-like methylation of the dio3 promoter, dio3 expression, and reproductive competence, revealing a dynamic and reversible mechanism of DNA methylation in the mammalian brain that plays a central role in physiological orientation in time.

Age- and sex-dependent DNA hypomethylation controlled by growth hormone in mouse liver

In mammals, differences in liver function and aging have been observed between sexes; however, the epigenetic mechanisms underlying such differences remain largely unexplored. In this study, we investigated sex- and age-dependent DNA methylation status in the mouse liver. We analyzed 90 known sex-differentially expressed genes, and identified sex-dependent methylation in Zfp809, Hsd3b5, Treh, Cxcl11, Cyp17a1, and Nnmt genes. After 4 weeks of age, we noted the gradual establishment of sex-dependent hypomethylation in each of these genes in either males or females. The exposure of male mice to female-like growth hormone (GH) profile repressed male-predominant hypomethylation and promoted female-predominant hypomethylation. The occurrence of age-dependent hypomethylation, including at loci for which we also observed sex-dependent changes in DNA methylation, was accompanied by the downregulation of DNMT3A/B. In addition, we found that age-dependent hypomethylation was promoted through liver regeneration induced by partial hepatectomy, suggesting that DNMT activities were not enough to retain methylation levels. In conclusion, our results demonstrate that sex-dependent GH profiles influence the age-progressive hypomethylation under decreased DNMT3A/B levels in certain regions of the genome.

Sex-specific expression of estrogen receptors α and β and Kiss1 in the postnatal rat amygdala

The rodent amygdaloid complex is composed of numerous subnuclei important for the sex-specific regulation of sociosexual behavior. Although estrogen receptors (ERs) are critical for organizing functional and cytoarchitectural sex differences in these subnuclei, a detailed developmental profile of ER expression in the amygdaloid complex is not available. Moreover, the kisspeptin gene (Kiss1) was recently identified in the adult amygdala, but it remains unknown if it is expressed during development. To fill these data gaps, rat brains (5-7/group) were assessed on postnatal days (PNDs) 0, 2, 4, 7, and 19 for ER alpha (ERα; Esr1), beta (ERβ; Esr2), and Kiss1 expression using in situ hybridization. Expression was quantified in the posterodorsal portion of the medial amygdala posterodorsal (MePD), lateral (PLCo), and medial (PMCo) components of the posterior cortical nucleus, and the amygdalohippocampal area (AHi). ERα expression was high throughout the amygdala at birth, but sexually dimorphic only in the AHi. ERα expression in the MePD and the PLCo showed a U-shaped expression pattern over time. In the PMCo, ERα expression decreased from PND 2 and remained low through PND 19. Sexually dimorphic expression of ERβ in the MePD was observed on PND 0, with higher levels in females, but reversed by PND 4 due to declining levels in females. No Kiss1 signal was observed in the postnatal amygdala, suggesting that expression arises after puberty. These data reveal that ER expression is region-specific within the neonatal amygdala. These differences likely contribute to sex differences in sociosexual behavior across the lifespan.