Low-dose thyroxine attenuates autism-associated adverse effects of fetal alcohol in male offspring's social behavior and hippocampal gene expression

Upregulation of RasGRF1 ameliorates spatial cognitive dysfunction in mice after chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion (CCH)-mediated cognitive impairment is a serious problem worldwide. However, given its complexity, the underlying mechanisms by which CCH induces cognitive dysfunction remain unclear, resulting in a lack of effective treatments. In this study, we aimed to determine whether changes in the expression of RasGRF1, an important protein associated with cognition and synaptic plasticity, underlie the associated impairments in cognition after CCH. We found that RasGRF1 levels markedly decreased following CCH. Through prediction and validation studies, we observed that miRNA-323-3p was upregulated after CCH and could bind to the 3'-untranslated region of Rasgrf1 mRNA and regulate its expression in vitro. Moreover, the inhibition of miRNA-323-3p upregulated Rasgrf1 expression in the hippocampus after CCH, which was reversed by Rasgrf1 siRNA. This suggests that miRNA-323-3p is an important regulator of Rasgrf1. The Morris water maze and Y maze tests showed that miRNA-323-3p inhibition and Rasgrf1 upregulation improved spatial learning and memory, and electrophysiological measurements revealed deficits in long-term potentiation after CCH that were reversed by Rasgrf1 upregulation. Dendritic spine density and mature mushroom spine density were also improved after miRNA-323-3p inhibition and Rasgrf1 upregulation. Furthermore, Rasgrf1 upregulation by miRNA-323-3p inhibition improved dendritic spine density and mature mushroom spine density and ameliorated the deterioration of synapses and postsynaptic density. Overall, RasGRF1 regulation attenuated cognitive impairment, helped maintain structural and functional synaptic plasticity, and prevented synapse deterioration after CCH. These results suggest that Rasgrf1 downregulation by miRNA-323-3p plays an important role in cognitive impairment after CCH. Thus, RasGRF1 and miRNA-323-3p may represent potential therapeutic targets for cognitive impairment after CCH.

Sex-Specific Whole-Transcriptome Analysis in the Cerebral Cortex of FAE Offspring

Fetal alcohol spectrum disorders (FASDs) are associated with systemic inflammation and neurodevelopmental abnormalities. Several candidate genes were found to be associated with fetal alcohol exposure (FAE)-associated behaviors, but a sex-specific complete transcriptomic analysis was not performed at the adult stage. Recent studies have shown that they are regulated at the developmental stage. However, the sex-specific role of RNA in FAE offspring brain development and function has not been studied yet. Here, we carried out the first systematic RNA profiling by utilizing a high-throughput transcriptomic (RNA-seq) approach in response to FAE in the brain cortex of male and female offspring at adulthood (P60). Our RNA-seq data analysis suggests that the changes in RNA expression in response to FAE are marked sex-specific. We show that the genes Muc3a, Pttg1, Rec8, Clcnka, Capn11, and pnp2 exhibit significantly higher expression in the male offspring than in the female offspring at P60. FAE female mouse brain sequencing data also show an increased expression of Eno1, Tpm3, and Pcdhb2 compared to male offspring. We performed a pathway analysis using a commercial software package (Ingenuity Pathway Analysis). We found that the sex-specific top regulator genes (Rictor, Gaba, Fmri, Mlxipl) are highly associated with eIF2 (translation initiation), synaptogenesis (the formation of synapses between neurons in the nervous system), sirtuin (metabolic regulation), and estrogen receptor (involved in obesity, aging, and cancer) signaling. Taken together, our transcriptomic results demonstrate that FAE differentially alters RNA expression in the adult brain in a sex-specific manner.

Investigation of a derived adverse outcome pathway (AOP) network for endocrine-mediated perturbations

An adverse outcome pathway (AOP) is a compact representation of the available mechanistic information on observed adverse effects upon environmental exposure. Sharing of events across individual AOPs has led to the emergence of AOP networks. Since AOP networks are expected to be functional units of toxicity prediction, there is current interest in their development tailored to specific research question or regulatory problem. To this end, we have developed a detailed workflow to construct an endocrine-relevant AOP (ED-AOP) network based on the existing information available in AOP-Wiki. We propose a cumulative weight of evidence (WoE) score for each ED-AOP based on the WoE scores assigned to key event relationships (KERs) by AOP-Wiki, revealing gaps in AOP development. Connectivity analysis of the ED-AOP network comprising 48 AOPs reveals 7 connected components and 12 isolated AOPs. Subsequently, we apply standard network measures to perform an in-depth analysis of the two largest connected components of the ED-AOP network. Notably, the graph-theoretic analyses led to the identification of important events including points of convergence or divergence in the ED-AOP network. These findings can suggest potential adverse outcomes and facilitate the development of new endpoints or assays for chemical risk assessment. Detailed analysis of the largest component in the ED-AOP network gives insights on the systems-level perturbations caused by endocrine disruption, emergent paths, and stressor-event associations. In sum, the derived ED-AOP network can provide a broader view of the biological events disrupted by endocrine disruption, as well as facilitate better risk assessment of environmental chemicals.

Potential roles of imprinted genes in the teratogenic effects of alcohol on the placenta, somatic growth, and the developing brain

Despite several decades of research and prevention efforts, fetal alcohol spectrum disorders (FASD) remain the most common preventable cause of neurodevelopmental disabilities worldwide. Animal and human studies have implicated fetal alcohol-induced alterations in epigenetic programming as a chief mechanism in FASD. Several studies have demonstrated fetal alcohol-related alterations in methylation and expression of imprinted genes in placental, brain, and embryonic tissue. Imprinted genes are epigenetically regulated in a parent-of-origin-specific manner, in which only the maternal or paternal allele is expressed, and the other allele is silenced. The chief functions of imprinted genes are in placental development, somatic growth, and neurobehavior-three domains characteristically affected in FASD. In this review, we summarize the growing body of literature characterizing prenatal alcohol-related alterations in imprinted gene methylation and/or expression and discuss potential mechanistic roles for these alterations in the teratogenic effects of prenatal alcohol exposure. Future research is needed to examine potential physiologic mechanisms by which alterations in imprinted genes disrupt development in FASD, which may, in turn, elucidate novel targets for intervention. Furthermore, mechanistic alterations in imprinted gene expression and/or methylation in FASD may inform screening assays that identify individuals with FASD neurobehavioral deficits who may benefit from early interventions.

High Mobility Group Box 1/Toll-like Receptor 4 Signaling Increases GABRB3 Expression in Alcohol Exposure

INTRODUCTION

Prefrontal cortex (PFC) and striatal neurotransmitter homeostasis is affected by alcohol dependence. In this study, the microarray dataset from the Gene Expression Omnibus (GEO) database were downloaded. The prefrontal and striatum data were cross-analyzed to reveal the co-effects of alcohol dependence on the two brain regions of mice.

METHODS

The GSE123114 microarray profile was downloaded from the GEO database, and differentially expressed genes (DEGs) between the two groups were acquired by GEO2R. KEGG analyses were performed to identify the pivotal pathways of these DEGs. Key differential gene expressions and their mechanism associated with alcohol exposure were investigated by an intraperitoneal alcohol model.

RESULTS

A total of 13 overlapping DEGs from the PFC and striatal datasets of the GSE123114 microarray profile were identified, and they were significantly enriched in the morphine addiction pathway. The transcript levels and protein expression of Gabrb3 were consistent with the microarray data both in the PFC and striatum. The transcript levels of HMGB1, TLR4, TNFα and IL-1β were upregulated in the PFC and striatum of mice in the alcohol group. The HMGB1 inhibitor decreased Gabrb3 transcript and protein levels as well as TNFα and IL-1β transcript levels both in the PFC and striatum in the intraperitoneal alcohol model mice.

DISCUSSION

Through the reanalysis of GSE123114 microarray profile, we found that Gabrb3 is a key gene associated with alcohol exposure. In further experiments, our findings suggest that alcohol exposure modulates Gabrb3 expression through the HMGB1/TLR4 pathway. Moreover, inflammation-associated factors, such as IL-1β and TNFα, may be related to the HMGB1/TLR4-mediated regulation of GABRB3 expression in alcohol exposure.

Prenatal Alcohol Exposure in Rats Diminishes Postnatal Cxcl16 Chemokine Ligand Brain Expression

Maternal ethanol consumption during pregnancy is one of the main causes of Neurodevelopmental disorders (NDD). Prenatal alcohol exposure (PAE) produces several adverse manifestations. Even low or moderate intake has been associated with long-lasting behavioral and cognitive impairment in offspring. In this study we examined the gene expression profile in the rat nucleus accumbens using microarrays, comparing animals exposed prenatally to ethanol and controls. Microarray gene expression showed an overall downward regulatory effect of PAE. Gene cluster analysis reveals that the gene groups most affected are related to transcription regulation, transcription factors and homeobox genes. We focus on the expression of the C-X-C motif chemokine ligand 16 (Cxcl16) which was differentially expressed. There is a significant reduction in the expression of this chemokine throughout the brain under PAE conditions, evidenced here by quantitative polymerase chain reaction qPCR and immunohistochemistry. Chemokines are involved in neuroprotection and implicated in alcohol-induced brain damage and neuroinflammation in the developing central nervous system (CNS), therefore, the significance of the overall decrease in Cxcl16 expression in the brain as a consequence of PAE may reflect a reduced ability in neuroprotection against subsequent conditions, such as excitotoxic damage, inflammatory processes or even hypoxic-ischemic insult.

No Dataset Left Behind: Mechanistic Insights into Thyroid Receptor Signaling Through Transcriptomic Consensome Meta-Analysis

Background: Discovery-scale omics datasets relevant to thyroid receptors (TRs) and their physiological and synthetic bioactive small-molecule ligands allow for genome-wide interrogation of TR-regulated genes. These datasets have considerable collective value as a reference resource to allow researchers to routinely generate hypotheses addressing the mechanisms underlying the cell biology and physiology of TR signaling in normal and disease states. Methods: Here, we searched the Gene Expression Omnibus database to identify a population of publicly archived transcriptomic datasets involving genetic or pharmacological manipulation of either TR isoform in a mouse tissue or cell line. After initial quality control, samples were organized into contrasts (experiments), and transcript differential expression values and associated measures of significance were generated and committed to a consensome (for consensus omics) meta-analysis pipeline. To gain insight into tissue-selective functions of TRs, we generated liver- and central nervous system (CNS)-specific consensomes and identified evidence for genes that were selectively responsive to TR signaling in each organ. Results: The TR transcriptomic consensome ranks genes based on the frequency of their significant differential expression over the entire group of experiments. The TR consensome assigns elevated rankings both to known TR-regulated genes and to genes previously uncharacterized as TR-regulated, which shed mechanistic light on known cellular and physiological roles of TR signaling in different organs. We identify evidence for unreported genomic targets of TR signaling for which it exhibits strikingly distinct regulatory preferences in the liver and CNS. Moreover, the intersection of the TR consensome with consensomes for other cellular receptors sheds light on transcripts potentially mediating crosstalk between TRs and these other signaling paradigms. Conclusions: The mouse TR datasets and consensomes are freely available in the Signaling Pathways Project website for hypothesis generation, data validation, and modeling of novel mechanisms of TR regulation of gene expression. Our results demonstrate the insights into the mechanistic basis of thyroid hormone action that can arise from an ongoing commitment on the part of the research community to the deposition of discovery-scale datasets.

Chronic Ethanol Exposure Alters DNA Methylation in Neural Stem Cells: Role of Mouse Strain and Sex

Prenatal alcohol exposure (PAE) is considered as a risk factor for the development of fetal alcohol spectrum disorders (FASD). Evidence indicates that PAE affects epigenetic mechanisms (such as DNA methylation) and alters the normal differentiation and development of neural stem cells (NSC) in the fetal brain. However, PAE effects depend on several factors such as sex and strain of the studied subjects. Here, we investigated whether murine sex and strain contribute to the effects of chronic ethanol exposure on DNA methylation machinery of differentiating NSC. Further, the effects of PAE on glial lineage (including both astrocytes and oligodendrocytes) in a sex- and strain-dependent manner have not been studied yet. To examine the effects of chronic ethanol exposure on gliogenesis, we exposed differentiating NSC to glio-inductive culture conditions. Applying a standard in vitro model system, we treated male and female differentiating NSC (obtained from the forebrain of CD1 and C57BL/6 embryos at embryonic day 14.5) with chronic ethanol exposure (70 mM) for 8 days. We show that ethanol induces global DNA hypomethylation, while altering the expression of DNA methylation-related genes in a sex- and strain-specific manner. The observed change in cellular DNA methylation levels was associated with altered expression of glial markers CNPASE, GFAP, and OLIG2 in CD1 (but not C57BL/6) cells. We conclude that the impact of ethanol effect on DNA methylation is dependent on cellular sex and strain. Also, ethanol impact on neural stem cell fate commitment was only detected in cells isolated from CD1 mouse strain, but not in C57BL/6 cells. The results of the current study provide evidence that sex and strain of rodents (C57BL/6 and CD1) during gestation are important factors, which affect alcohol effects on NSC differentiation and DNA methylation. Results of this study may also help in interpreting data on the developmental toxicity of many compounds during the gestational period.

Hippocampal transcriptome reveals novel targets of FASD pathogenesis

INTRODUCTION

Prenatal alcohol exposure can contribute to fetal alcohol spectrum disorders (FASD), characterized by a myriad of developmental impairments affecting behavior and cognition. Studies show that many of these functional impairments are associated with the hippocampus, a structure exhibiting exquisite vulnerability to developmental alcohol exposure and critically implicated in learning and memory; however, mechanisms underlying alcohol-induced hippocampal deficits remain poorly understood. By utilizing a high-throughput RNA-sequencing (RNA-seq) approach to address the neurobiological and molecular basis of prenatal alcohol-induced hippocampal functional deficits, we hypothesized that chronic binge prenatal alcohol exposure alters gene expression and global molecular pathways in the fetal hippocampus.

METHODS

Timed-pregnant Sprague-Dawley rats were randomly assigned to a pair-fed control (PF) or binge alcohol (ALC) treatment group on gestational day (GD) 4. ALC dams acclimatized from GDs 5-10 with a daily treatment of 4.5 g/kg alcohol and subsequently received 6 g/kg on GDs 11-20. PF dams received a once daily maltose dextrin gavage on GDs 5-20, isocalorically matching ALC counterparts. On GD 21, bilateral hippocampi were dissected, flash frozen, and stored at -80° C. Total RNA was then isolated from homogenized tissues. Samples were normalized to ~4nM and pooled equally. Sequencing was performed by Illumina NextSeq 500 on a 75 cycle, single-end sequencing run.

RESULTS

RNA-seq identified 13,388 genes, of these, 76 genes showed a significant difference (p < 0.05, log2 fold change ≥2) in expression between the PF and ALC groups. Forty-nine genes showed sex-dependent dysregulation; IPA analysis showed among female offspring, dysregulated pathways included proline and citrulline biosynthesis, whereas in males, xenobiotic metabolism signaling and alaninine biosynthesis etc. were altered.

CONCLUSION

We conclude that chronic binge alcohol exposure during pregnancy dysregulates fetal hippocampal gene expression in a sex-specific manner. Identification of subtle, transcriptome-level dysregulation in hippocampal molecular pathways offers potential mechanistic insights underlying FASD pathogenesis.

Oxidative stress and DNA damage in the mechanism of fetal alcohol spectrum disorders

This review covers molecular mechanisms involving oxidative stress and DNA damage that may contribute to morphological and functional developmental disorders in animal models resulting from exposure to alcohol (ethanol, EtOH) in utero or in embryo culture. Components covered include: (a) a brief overview of EtOH metabolism and embryopathic mechanisms other than oxidative stress; (b) mechanisms within the embryo and fetal brain by which EtOH increases the formation of reactive oxygen species (ROS); (c) critical embryonic/fetal antioxidative enzymes and substrates that detoxify ROS; (d) mechanisms by which ROS can alter development, including ROS-mediated signal transduction and oxidative DNA damage, the latter of which leads to pathogenic genetic (mutations) and epigenetic changes; (e) pathways of DNA repair that mitigate the pathogenic effects of DNA damage; (f) related indirect mechanisms by which EtOH enhances risk, for example by enhancing the degradation of some DNA repair proteins; and, (g) embryonic/fetal pathways like NRF2 that regulate the levels of many of the above components. Particular attention is paid to studies in which chemical and/or genetic manipulation of the above mechanisms has been shown to alter the ability of EtOH to adversely affect development. Alterations in the above components are also discussed in terms of: (a) individual embryonic and fetal determinants of risk and (b) potential risk biomarkers and mitigating strategies. FASD risk is likely increased in progeny which/who are biochemically predisposed via genetic and/or environmental mechanisms, including enhanced pathways for ROS formation and/or deficient pathways for ROS detoxification or DNA repair.

Deletion of TLR-4 attenuates fetal alcohol exposure-induced gene expression and social interaction deficits

Fetal alcohol spectrum disorders (FASD) are associated with social interaction behavior and gastrointestinal (GI) abnormalities. These abnormal behaviors and GI abnormalities overlap with autism spectrum disorder (ASD). We investigated the effect of fetal alcohol exposure (FAE) on social interaction deficits (hallmark of autism) in mice. Evidence indicates that exogenous lipopolysaccharide (LPS) administration during gestation induces autism-like behavior in the offspring. LPS regulates the expression of genes underlying differentiation, immune function, myelination, and synaptogenesis in fetal brain by the LPS receptor, TLR-4-dependent mechanism. In this study, we evaluated the role of TLR-4 in FAE-induced social behavior deficit. WT and TLR4^-/- pregnant mice were fed Lieber-DeCarli liquid diet with or without ethanol. The control group was pair-fed with an isocaloric diet. Social behavior was tested in the adult offspring at postnatal day 60. Frontal cortex mRNA expression of autistic candidate genes (Ube3a, Gabrb3, Mecp2) and inflammatory cytokine genes (IL-1β, IL-6, TNF-α) were measured by RT-qPCR. Adult male offspring of ethanol-fed WT dams showed low birth weight compared to offspring of pair-fed WT dams. However, their body weights at adulthood were greater compared to the body weights of offspring of pair-fed WT dams. There were no body weight differences in offspring of TLR4^-/- dams. Social interaction deficit was observed only in male offspring of ethanol-fed WT dams, but it was not observed in both male and female offspring of ethanol-fed TLR4^-/- dams. Expressions of autism candidate genes, Gabrb3 and Ube3a, were elevated, while that of the Mecp2 gene was suppressed in the frontal cortex of male, but not female, offspring of ethanol-fed WT mice. The expressions of inflammatory cytokine genes, IL-1β, IL-6, and TNF-α, were also significantly increased in the frontal cortex of male, but not female, offspring of ethanol-fed dams. The changes in the expression of autistic and cytokine genes were unaffected in the offspring of ethanol-fed TLR4^-/- dams. These data also indicate that TLR4 mediates FAE-induced changes in social interactions and gene expression in brain, suggesting that ethanol-induced LPS absorption from the maternal gut may be involved in gene expression changes in the fetal brain.

Speech Impairment in Boys With Fetal Alcohol Spectrum Disorders

BACKGROUND

Fetal alcohol spectrum disorders (FASD) are a highly prevalent spectrum of patterns of congenital defects resulting from prenatal exposure to alcohol. Approximately 90% of the cases involve speech impairment. Yet, to date, no detailed symptom profiles nor dedicated treatment plans are available for this population.

PURPOSE

This study set out to chart the speech and speech motor characteristics in boys with FASD to profile the concomitant speech impairment and identify possible underlying mechanisms.

METHOD

Ten boys with FASD (4.5-10.3 years old) and 26 typically developing children (4.1-8.7 years old; 14 boys, 12 girls) participated in the study. Speech production and perception, and oral motor data were collected by standardized tests.

RESULTS

The boys with FASD showed reduced scores on all tasks as well as a deviant pattern of correlations between production and perception tasks and intelligibility compared with the typically developing children. Speech motor profiles showed specific problems with nonword repetition and tongue control.

CONCLUSIONS

Findings indicate that the speech impairment in boys with FASD results from a combination of deficits in multiple subsystems and should be approached as a disorder rather than a developmental delay. The results suggest that reduced speech motor planning/programming, auditory discrimination, and oral motor abilities should be considered in long-term, individually tailored treatment.

Hippocampus-dependent memory and allele-specific gene expression in adult offspring of alcohol-consuming dams after neonatal treatment with thyroxin or metformin

Fetal alcohol spectrum disorder (FASD), the result of fetal alcohol exposure (FAE), affects 2-11% of children worldwide, with no effective treatments. Hippocampus-based learning and memory deficits are key symptoms of FASD. Our previous studies show hypothyroxinemia and hyperglycemia of the alcohol-consuming pregnant rat, which likely affects fetal neurodevelopment. We administered vehicle, thyroxine (T4) or metformin to neonatal rats post FAE and rats were tested in the hippocampus-dependent contextual fear-conditioning paradigm in adulthood. Both T4 and metformin alleviated contextual fear memory deficit induced by FAE, and reversed the hippocampal expression changes in the thyroid hormone-inactivating enzyme, deiodinase-III (Dio3) and insulin-like growth factor 2 (Igf2), genes that are known to modulate memory processes. Neonatal T4 restored maternal allelic expressions of the imprinted Dio3 and Igf2 in the adult male hippocampus, while metformin restored FAE-caused changes in Igf2 expression only. The decreased hippocampal expression of DNA methyltransferase 1 (Dnmt1) that maintains the imprinting of Dio3 and Igf2 during development was normalized by both treatments. Administering Dnmt1 inhibitor to control neonates resulted in FAE-like deficits in fear memory and hippocampal allele-specific expression of Igf2, which were reversed by metformin. We propose that neonatal administration of T4 and metformin post FAE affect memory via elevating Dnmt1 and consequently normalizing hippocampal Dio3 and Igf2 expressions in the adult offspring. The present results indicate that T4 and metformin, administered during the neonatal period that is equivalent to the third trimester of human pregnancy, are potential treatments for FASD and conceivably for other neurodevelopmental disorders with cognitive deficits.

The Type 3 Deiodinase: Epigenetic Control of Brain Thyroid Hormone Action and Neurological Function

Thyroid hormones (THs) influence multiple processes in the developing and adult central nervous system, and their local availability needs to be maintained at levels that are tailored to the requirements of their biological targets. The local complement of TH transporters, deiodinase enzymes, and receptors is critical to ensure specific levels of TH action in neural cells. The type 3 iodothyronine deiodinase (DIO3) inactivates THs and is highly present in the developing and adult brain, where it limits their availability and action. DIO3 deficiency in mice results in a host of neurodevelopmental and behavioral abnormalities, demonstrating the deleterious effects of TH excess, and revealing the critical role of DIO3 in the regulation of TH action in the brain. The fact the Dio3 is an imprinted gene and that its allelic expression pattern varies across brain regions and during development introduces an additional level of control to deliver specific levels of hormone action in the central nervous system (CNS). The sensitive epigenetic nature of the mechanisms controlling the genomic imprinting of Dio3 renders brain TH action particularly susceptible to disruption due to exogenous treatments and environmental exposures, with potential implications for the etiology of human neurodevelopmental disorders.

Thyroid Function in Pregnant Women With Moderate to Severe Alcohol Consumption Is Related to Infant Developmental Outcomes

INTRODUCTION

Fetal alcohol spectrum disorders (FASD) have an estimated global prevalence of 2-5% of births, but prevalence is reported to be as high as 15.5% for FASD in certain high-risk communities in South Africa. Preclinical studies demonstrate that alcohol consumption during pregnancy interferes with thyroid hormone availability and function and negatively impacts exposed offspring. Very little is currently reported on this phenomenon in humans.

METHODS

This pilot study was embedded in the Drakenstein Child Health Study, a multi-disciplinary longitudinal birth cohort study investigating the early biological and psychosocial determinants of child health in South Africa. Twenty one mothers and their children with moderate-severe prenatal alcohol exposure (PAE) and 19 mothers and their children with no alcohol exposure were investigated. Maternal exposure history and blood samples were collected in mid-pregnancy and analyzed for serum-free thyroxin (FT4), free triiodothyronine (FT3), and thyroid stimulating hormone (TSH). Children were assessed with formally measured growth parameters and development was evaluated using the Bayley III Scales of Infant and Toddler Development (BSID III) at 6 and 24 months of age.

RESULTS

While there were no significant differences in serum TSH and FT4 between groups, FT3 levels were significantly higher in mothers with moderate-severe prenatal alcohol use. In abstinent pregnant women, levels of FT4 were significantly correlated with infants' scores on cognitive measures at 6 and 24 months of age and with levels of gross motor skills at 24 months. However, in mothers with alcohol use, FT4 levels were not correlated with any cognitive or motor skills, but FT3 levels were significantly associated with scores on children's social-emotional development at 24 months of age.

DISCUSSION

Thyroid function in PAE is sufficiently disrupted to lead to alterations in serum FT3 levels. The contrast in findings between PAE and abstinent dyads in their association of maternal thyroid function and infant development further suggests that such disruption is present and may contribute to adverse neurodevelopment. Further work is needed to determine the relationship between peripheral thyroid indices during pregnancy and neurodevelopmental outcomes in the context of PAE.

Fetal oxidative stress mechanisms of neurodevelopmental deficits and exacerbation by ethanol and methamphetamine

In utero exposure of mouse progeny to alcohol (ethanol, EtOH) and methamphetamine (METH) causes substantial postnatal neurodevelopmental deficits. One emerging pathogenic mechanism underlying these deficits involves fetal brain production of reactive oxygen species (ROS) that alter signal transduction, and/or oxidatively damage cellular macromolecules like lipids, proteins, and DNA, the latter leading to altered gene expression, likely via non-mutagenic mechanisms. Even physiological levels of fetal ROS production can be pathogenic in biochemically predisposed progeny, and ROS formation can be enhanced by drugs like EtOH and METH, via activation/induction of ROS-producing NADPH oxidases (NOX), drug bioactivation to free radical intermediates by prostaglandin H synthases (PHS), and other mechanisms. Antioxidative enzymes, like catalase in the fetal brain, while low, provide critical protection. Oxidatively damaged DNA is normally rapidly repaired, and fetal deficiencies in several DNA repair proteins, including oxoguanine glycosylase 1 (OGG1) and breast cancer protein 1 (BRCA1), enhance the risk of drug-initiated postnatal neurodevelopmental deficits, and in some cases deficits in untreated progeny, the latter of which may be relevant to conditions like autism spectrum disorders (ASD). Risk is further regulated by fetal nuclear factor erythroid 2-related factor 2 (Nrf2), a ROS-sensing protein that upregulates an array of proteins, including antioxidative enzymes and DNA repair proteins. Imbalances between conceptal pathways for ROS formation, versus those for ROS detoxification and DNA repair, are important determinants of risk. Birth Defects Research (Part C) 108:108-130, 2016. © 2016 Wiley Periodicals, Inc.

Chromatin Switches during Neural Cell Differentiation and Their Dysregulation by Prenatal Alcohol Exposure

Prenatal alcohol exposure causes persistent neuropsychiatric deficits included under the term fetal alcohol spectrum disorders (FASD). Cellular identity emerges from a cascade of intrinsic and extrinsic (involving cell-cell interactions and signaling) processes that are partially initiated and maintained through changes in chromatin structure. Prenatal alcohol exposure influences neuronal and astrocyte development, permanently altering brain connectivity. Prenatal alcohol exposure also alters chromatin structure through histone and DNA modifications. However, the data linking alcohol-induced differentiation changes with developmental alterations in chromatin structure remain to be elucidated. In the first part of this review, we discuss the sequence of chromatin structural changes involved in neural cell differentiation during normal development. We then discuss the effects of prenatal alcohol on developmental histone modifications and DNA methylation in the context of neurogenesis and astrogliogenesis. We attempt to synthesize the developmental literature with the FASD literature, proposing that alcohol-induced changes to chromatin structure account for altered neurogenesis and astrogliogenesis as well as altered neuron and astrocyte differentiation. Together these changes may contribute to the cognitive and behavioral abnormalities in FASD. Future studies using standardized alcohol exposure paradigms at specific developmental stages will advance the understanding of how chromatin structural changes impact neural cell fate and maturation in FASD.

Social Order: Using The Sequential Structure of Social Interaction to Discriminate Abnormal Social Behavior in the Rat

Social interactions form the basis of a broad range of functions related to survival and mating. The complexity of social behaviors and the flexibility required for normal social interactions make social behavior particularly susceptible to disruption. The consequences of developmental insults in the social domain and the associated neurobiological factors are commonly studied in rodents. Though methods for investigating social interactions in the laboratory are diverse, animals are typically placed together in an apparatus for a brief period (under 30 min) and allowed to interact freely while behavior is recorded for subsequent analysis. A standard approach to the analysis of social behavior involves quantification of the frequency and duration of individual social behaviors. This approach provides information about the allocation of time to particular behaviors within a session, which is typically sufficient for detection of robust alterations in behavior. Virtually all social species, however, display complex sequences of social behavior that are not captured in the quantification of individual behaviors. Sequences of behavior may provide more sensitive indicators of disruptions in social behavior. Sophisticated analysis systems for quantification of behavior sequences have been available for many years; however, the required training and time to complete these analyses represent significant barriers to high-throughput assessments. We present a simple approach to the quantification of behavioral sequences that requires minimal additional analytical steps after individual behaviors are coded. We implement this approach to identify altered social behavior in rats exposed to alcohol during prenatal development, and show that the frequency of several pairwise sequences of behavior discriminate controls from ethanol-exposed rats when the frequency of individual behaviors involved in those sequences does not. Thus, the approach described here may be useful in detecting subtle deficits in the social domain and identifying neural circuits involved in the organization of social behavior.

Thyroid dysfunction in children with autism spectrum disorder is associated with folate receptor α autoimmune disorder

Folate receptor α (FRα) autoantibodies (FRAAs) are prevalent in autism spectrum disorder (ASD). FRAAs disrupt folate transport across the blood-brain barrier by binding to the FRα. Thyroid dysfunction is frequently found in children with ASD. We measured blocking and binding FRAAs and thyroid-stimulating hormone (TSH), free thyroxine (T4) (FT4), total triiodothyronine (T3) (TT3), reverse T3 (rT3), thyroid-releasing hormone (TRH) and other metabolites in 87 children with ASD, 84 of whom also underwent behaviour and cognition testing and in 42 of whom FRAAs, TSH and FT4 were measured at two time points. To better understand the significance of the FRα in relation to thyroid development, we examined FRα expression on prenatal and postnatal thyroid. TSH, TT3 and rT3 were above the normal range in 7%, 33% and 51% of the participants and TRH was below the normal range in 13% of the participants. FT4 was rarely outside the normal range. TSH concentration was positively and the FT4/TSH, TT3/TSH and rT3/TSH ratios were inversely related to blocking FRAA titres. On repeated measurements, changes in TSH and FT4/TSH ratio were found to correspond to changes in blocking FRAA titres. TSH and the FT4/TSH, TT3/TSH and rT3/TSH ratios were related to irritability on the Aberrant Behavior Checklist and several scales of the Social Responsiveness Scale (SRS), whereas TT3 was associated with SRS subscales and TRH was related to Vineland Adaptive Behavior Scale subscales. The thyroid showed significant FRα expression during the early prenatal period, although expression decreased significantly in later gestation and postnatal thyroid tissue. The results of the present study suggest that thyroid dysfunction in ASD may be related to blocking FRAA. The high expression of FRα in the early foetal thyroid suggests that foetal and neonatal exposure to maternal FRAAs could affect the development of the thyroid and may contribute to the pathology in ASD.

Ifenprodil infusion in agranular insular cortex alters social behavior and vocalizations in rats exposed to moderate levels of ethanol during prenatal development

Moderate exposure to alcohol during development leads to subtle neurobiological and behavioral effects classified under the umbrella term fetal alcohol spectrum disorders (FASDs). Alterations in social behaviors are a frequently observed consequence of maternal drinking, as children with FASDs display inappropriate aggressive behaviors and altered responses to social cues. Rodent models of FASDs mimic the behavioral alterations seen in humans, with rats exposed to ethanol during development displaying increased aggressive behaviors, decreased social investigation, and altered play behavior. Work from our laboratory has observed increased wrestling behavior in adult male rats following prenatal alcohol exposure (PAE), and increased expression of GluN2B-containing NMDA receptors in the agranular insular cortex (AIC). This study was undertaken to determine if ifenprodil, a GluN2B preferring negative allosteric modulator, has a significant effect on social behaviors in PAE rats. Using a voluntary ethanol exposure paradigm, rat dams were allowed to drink a saccharin-sweetened solution of either 0% or 5% ethanol throughout gestation. Offspring at 6-8 months of age were implanted with cannulae into AIC. Animals were isolated for 24h before ifenprodil or vehicle was infused into AIC, and after 15min they were recorded in a social interaction chamber. Ifenprodil treatment altered aspects of wrestling, social investigatory behaviors, and ultrasonic vocalizations in rats exposed to ethanol during development that were not observed in control animals. These data indicate that GluN2B-containing NMDA receptors in AIC play a role in social behaviors and may underlie alterations in behavior and vocalizations observed in PAE animals.

Effects of sex and housing on social, spatial, and motor behavior in adult rats exposed to moderate levels of alcohol during prenatal development

Persistent deficits in social behavior, motor behavior, and behavioral flexibility are among the major negative consequences associated with exposure to ethanol during prenatal development. Prior work from our laboratory has linked moderate prenatal alcohol exposure (PAE) in the rat to deficits in these behavioral domains, which depend upon the ventrolateral frontal cortex (Hamilton et al., 2014) [20]. Manipulations of the social environment cause modifications of dendritic morphology and experience-dependent immediate early gene expression in ventrolateral frontal cortex (Hamilton et al., 2010) [19], and may yield positive behavioral outcomes following PAE. In the present study we evaluated the effects of housing PAE rats with non-exposed control rats on adult behavior. Rats of both sexes were either paired with a partner from the same prenatal treatment condition (ethanol or saccharin) or from the opposite condition (mixed housing condition). At four months of age (∼3 months after the housing manipulation commenced), social behavior, tongue protrusion, and behavioral flexibility in the Morris water task were measured as in (Hamilton et al., 2014) [20]. The behavioral effects of moderate PAE were primarily limited to males and were not ameliorated by housing with a non-ethanol exposed partner. Unexpectedly, social behavior, motor behavior, and spatial flexibility were adversely affected in control rats housed with a PAE rat (i.e., in mixed housing), indicating that housing with a PAE rat has broad behavioral consequences beyond the social domain. These observations provide further evidence that moderate PAE negatively affects social behavior, and underscore the importance of considering potential negative effects of housing with PAE animals on the behavior of critical comparison groups.

Thyroxine administration prevents matrilineal intergenerational consequences of in utero ethanol exposure in rats

The neurodevelopmental fetal alcohol spectrum disorder (FASD) is characterized by cognitive and behavioral deficits in the offspring. Conferring the deficits to the next generation would increase overall FASD disease burden and prevention of this transmission could be highly significant. Prior studies showed the reversal of these behavioral deficits by low dose thyroxine (T4) supplementation to the ethanol-consuming mothers. Here we aim to identify whether prenatal ethanol (PE) exposure impairs hippocampus-dependent learning and memory in the second-generation (F2) progeny, and whether T4 administration to the ethanol-consuming dam can prevent it. Sprague-Dawley (S) dams received control diets (ad libitum and nutritional control) or ethanol containing liquid diet with and without simultaneous T4 (0.3mg/L diet) administration. Their offspring (SS F1) were mated with naive Brown Norway (B) males and females generating the SB F2 and BS F2 progeny. Hippocampus-dependent contextual fear memory and hippocampal expression of the thyroid hormone-regulated type 3 deiodinase, (Dio3) and neurogranin (Nrgn) were assessed. SS F1 PE-exposed females and their SB F2 progeny exhibited fear memory deficits. T4 administration to the mothers of F1 females reversed these deficits. Although SS F1 PE-exposed males also experienced fear memory deficit, this was neither transmitted to their BS F2 offspring nor reversed by prenatal T4 treatment. Hippocampal Dio3 and Nrgn expression showed similar pattern of changes. Grandmaternal ethanol consumption during pregnancy affects fear memory of the matrilineal second-generation progeny. Low dose T4 supplementation prevents this process likely via altering allele-specific and total expression of Dio3 in the hippocampus.

Modeling Fetal Alcohol Spectrum Disorder: Validating an Ex Vivo Primary Hippocampal Cell Culture System

BACKGROUND

Fetal alcohol spectrum disorder (FASD) is the leading nongenetic cause of mental retardation. There are no treatments for FASD to date. Preclinical in vivo and in vitro studies could help in identifying novel drug targets as for other diseases. Here, we describe an ex vivo model that combines the physiological advantages of prenatal ethanol (EtOH) exposure in vivo with the uniformity of primary fetal hippocampal culture to characterize the effects of prenatal EtOH. The insulin signaling pathways are known to be involved in hippocampal functions. Therefore, we compared the expression of insulin signaling pathway genes between fetal hippocampi (in vivo) and primary hippocampal culture (ex vivo). The similarity of prenatal EtOH effects in these 2 paradigms would deem the ex vivo culture acceptable to screen possible treatments for FASD.

METHODS

Pregnant Sprague-Dawley rats received 1 of 3 diets: ad libitum standard laboratory chow (control-C), isocaloric pair-fed (nutritional control), and EtOH containing liquid diets from gestational day (GD) 8. Fetal male and female hippocampi were collected either on GD21 (in vivo) or on GD18 for primary culture (ex vivo). Transcript levels of Igf2, Igf2r, Insr, Grb10, Rasgrf1, and Zac1 were measured by reverse transcription quantitative polymerase chain reaction.

RESULTS

Hippocampal transcript levels differed by prenatal treatment in both males and females with sex differences observed in the expression of Igf2 and Insr. The effect of prenatal EtOH on the hippocampal expression of the insulin pathway genes was parallel in the in vivo and the ex vivo conditions.

CONCLUSIONS

The similarity of gene expression changes in response to prenatal EtOH between the in vivo and the ex vivo conditions ascertains that these effects are already set in the fetal hippocampus at GD18. This strengthens the feasibility of the ex vivo primary hippocampal culture as a tool to test and screen candidate drug targets for FASD.

Epigenetic mechanisms: A possible link between autism spectrum disorders and fetal alcohol spectrum disorders

The etiology of autism spectrum disorders (ASDs) still remains unclear and seems to involve a considerable overlap between polygenic, epigenetic and environmental factors. We have summarized the current understanding of the interplay between gene expression dysregulation via epigenetic modifications and the potential epigenetic impact of environmental factors in neurodevelopmental deficits. Furthermore, we discuss the scientific controversies of the relationship between prenatal exposure to alcohol and alcohol-induced epigenetic dysregulations, and gene expression alterations which are associated with disrupted neural plasticity and causal pathways for ASDs. The review of the literature suggests that a better understanding of developmental epigenetics should contribute to furthering our comprehension of the etiology and pathogenesis of ASDs and fetal alcohol spectrum disorders.

The gestational foundation of sex differences in development and vulnerability

Despite long-standing interest in the role of sex on human development, the functional consequences of fetal sex on early development are not well-understood. Here we explore the gestational origins of sex as a moderator of development. In accordance with the focus of this special issue, we examine evidence for a sex differential in vulnerability to prenatal and perinatal risks. Exposures evaluated include those present in the external environment (e.g., lead, pesticides), those introduced by maternal behaviors (e.g., alcohol, opioid use), and those resulting from an adverse intrauterine environment (e.g., preterm birth). We also provide current knowledge on the degree to which sex differences in fetal neurobehavioral development (i.e., cardiac and motor patterns) are present prior to birth. Also considered are contemporaneous and persistent sex of fetus effects on the pregnant woman. Converging evidence confirms that infant and early childhood developmental outcomes of male fetuses exposed to prenatal and perinatal adversities are more highly impaired than those of female fetuses. In certain circumstances, male fetuses are both more frequently exposed to early adversities and more affected by them when exposed than are female fetuses. The mechanisms through which biological sex imparts vulnerability or protection on the developing nervous system are largely unknown. We consider models that implicate variation in maturation, placental functioning, and the neuroendocrine milieu as potential contributors. Many studies use sex as a control variable, some analyze and report main effects for sex, but those that report interaction terms for sex are scarce. As a result, the true scope of sex differences in vulnerability is unknown.

Moderate prenatal alcohol exposure enhances GluN2B containing NMDA receptor binding and ifenprodil sensitivity in rat agranular insular cortex

Prenatal exposure to alcohol affects the expression and function of glutamatergic neurotransmitter receptors in diverse brain regions. The present study was undertaken to fill a current gap in knowledge regarding the regional specificity of ethanol-related alterations in glutamatergic receptors in the frontal cortex. We quantified subregional expression and function of glutamatergic neurotransmitter receptors (AMPARs, NMDARs, GluN2B-containing NMDARs, mGluR1s, and mGluR5s) by radioligand binding in the agranular insular cortex (AID), lateral orbital area (LO), prelimbic cortex (PrL) and primary motor cortex (M1) of adult rats exposed to moderate levels of ethanol during prenatal development. Increased expression of GluN2B-containing NMDARs was observed in AID of ethanol-exposed rats compared to modest reductions in other regions. We subsequently performed slice electrophysiology measurements in a whole-cell patch-clamp preparation to quantify the sensitivity of evoked NMDAR-mediated excitatory postsynaptic currents (EPSCs) in layer II/III pyramidal neurons of AID to the GluN2B negative allosteric modulator ifenprodil. Consistent with increased GluN2B expression, ifenprodil caused a greater reduction in NMDAR-mediated EPSCs from prenatal alcohol-exposed rats than saccharin-exposed control animals. No alterations in AMPAR-mediated EPSCs or the ratio of AMPARs/NMDARs were observed. Together, these data indicate that moderate prenatal alcohol exposure has a significant and lasting impact on GluN2B-containing receptors in AID, which could help to explain ethanol-related alterations in learning and behaviors that depend on this region.

Ethanol deregulates Mecp2/MeCP2 in differentiating neural stem cells via interplay between 5-methylcytosine and 5-hydroxymethylcytosine at the Mecp2 regulatory elements

Methyl CpG Binding Protein 2 (MeCP2) is an important epigenetic factor in the brain. MeCP2 expression is affected by different environmental insults including alcohol exposure. Accumulating evidence supports the role of aberrant MeCP2 expression in ethanol exposure-induced neurological symptoms. However, the underlying molecular mechanisms of ethanol-induced MeCP2 deregulation remain elusive. To study the effect of ethanol on Mecp2/MeCP2 expression during neurodifferentiation, we established an in vitro model of ethanol exposure, using differentiating embryonic brain-derived neural stem cells (NSC). Previously, we demonstrated the impact of DNA methylation at the Mecp2 regulatory elements (REs) on Mecp2/MeCP2 expression in vitro and in vivo. Here, we studied whether altered DNA methylation at these REs is associated with the Mecp2/MeCP2 misexpression induced by ethanol. Binge-like and continuous ethanol exposure upregulated Mecp2/MeCP2, while ethanol withdrawal downregulated its expression. DNA methylation analysis by methylated DNA immunoprecipitation indicated that increased 5-hydroxymethylcytosine (5hmC) and decreased 5-methylcytosine (5mC) enrichment at specific REs were associated with upregulated Mecp2/MeCP2 following continuous ethanol exposure. The reduced Mecp2/MeCP2 expression upon ethanol withdrawal was associated with reduced 5hmC and increased 5mC enrichment at these REs. Moreover, ethanol altered global DNA methylation (5mC and 5hmC). Under the tested conditions, ethanol had minimal effects on NSC cell fate commitment, but caused changes in neuronal morphology and glial cell size. Taken together, our data represent an epigenetic mechanism for ethanol-mediated misexpression of Mecp2/MeCP2 in differentiating embryonic brain cells. We also show the potential role of DNA methylation and MeCP2 in alcohol-related neurological disorders, specifically Fetal Alcohol Spectrum Disorders.

Moderate prenatal alcohol exposure and quantification of social behavior in adult rats

Alterations in social behavior are among the major negative consequences observed in children with Fetal Alcohol Spectrum Disorders (FASDs). Several independent laboratories have demonstrated robust alterations in the social behavior of rodents exposed to alcohol during brain development across a wide range of exposure durations, timing, doses, and ages at the time of behavioral quantification. Prior work from this laboratory has identified reliable alterations in specific forms of social interaction following moderate prenatal alcohol exposure (PAE) in the rat that persist well into adulthood, including increased wrestling and decreased investigation. These behavioral alterations have been useful in identifying neural circuits altered by moderate PAE(1), and may hold importance for progressing toward a more complete understanding of the neural bases of PAE-related alterations in social behavior. This paper describes procedures for performing moderate PAE in which rat dams voluntarily consume ethanol or saccharin (control) throughout gestation, and measurement of social behaviors in adult offspring.

DNA modifications: function and applications in normal and disease States

Epigenetics refers to a variety of processes that have heritable effects on gene expression programs without changes in DNA sequence. Key players in epigenetic control are chemical modifications to DNA, histone, and non-histone chromosomal proteins, which establish a complex regulatory network that controls genome function. Methylation of DNA at the fifth position of cytosine in CpG dinucleotides (5-methylcytosine, 5mC), which is carried out by DNA methyltransferases, is commonly associated with gene silencing. However, high resolution mapping of DNA methylation has revealed that 5mC is enriched in exonic nucleosomes and at intron-exon junctions, suggesting a role of DNA methylation in the relationship between elongation and RNA splicing. Recent studies have increased our knowledge of another modification of DNA, 5-hydroxymethylcytosine (5hmC), which is a product of the ten-eleven translocation (TET) proteins converting 5mC to 5hmC. In this review, we will highlight current studies on the role of 5mC and 5hmC in regulating gene expression (using some aspects of brain development as examples). Further the roles of these modifications in detection of pathological states (type 2 diabetes, Rett syndrome, fetal alcohol spectrum disorders and teratogen exposure) will be discussed.

Hypothesis: genetic and epigenetic risk factors interact to modulate vulnerability and resilience to FASD

Fetal alcohol spectrum disorder (FASD) presents a collection of symptoms representing physiological and behavioral phenotypes caused by maternal alcohol consumption. Symptom severity is modified by genetic differences in fetal susceptibility and resistance as well as maternal genetic factors such as maternal alcohol sensitivity. Animal models demonstrate that both maternal and paternal genetics contribute to the variation in the fetus' vulnerability to alcohol exposure. Maternal and paternal genetics define the variations in these phenotypes even without the effect of alcohol in utero, as most of these traits are polygenic, non-Mendelian, in their inheritance. In addition, the epigenetic alterations that instigate the alcohol induced neurodevelopmental deficits can interact with the polygenic inheritance of respective traits. Here, based on specific examples, we present the hypothesis that the principles of non-Mendelian inheritance, or "exceptions" to Mendelian genetics, can be the driving force behind the severity of the prenatal alcohol-exposed individual's symptomology. One such exception is when maternal alleles lead to an altered intrauterine hormonal environment and, therefore, produce variations in the long-term consequences on the development of the alcohol-exposed fetus. Another exception is when epigenetic regulation of allele-specific gene expression generates disequilibrium between the maternal vs. paternal genetic contributions, and thereby, modifies the effect of prenatal alcohol exposure on the fetus. We propose that these situations in which one parent has an exaggerated influence over the offspring's vulnerability to prenatal alcohol are major contributing mechanisms responsible for the variations in the symptomology of FASD in the exposed generation and beyond.

Effects of moderate prenatal ethanol exposure and age on social behavior, spatial response perseveration errors and motor behavior

Persistent deficits in social behavior are among the major negative consequences associated with exposure to ethanol during prenatal development. Prior work from our laboratory has linked deficits in social behavior following moderate prenatal alcohol exposure (PAE) in the rat to functional alterations in the ventrolateral frontal cortex [21]. In addition to social behaviors, the regions comprising the ventrolateral frontal cortex are critical for diverse processes ranging from orofacial motor movements to flexible alteration of behavior in the face of changing consequences. The broader behavioral implications of altered ventrolateral frontal cortex function following moderate PAE have, however, not been examined. In the present study we evaluated the consequences of moderate PAE on social behavior, tongue protrusion, and flexibility in a variant of the Morris water task that required modification of a well-established spatial response. PAE rats displayed deficits in tongue protrusion, reduced flexibility in the spatial domain, increased wrestling, and decreased investigation, indicating that several behaviors associated with ventrolateral frontal cortex function are impaired following moderate PAE. A linear discriminant analysis revealed that measures of wrestling and tongue protrusion provided the best discrimination of PAE rats from saccharin-exposed control rats. We also evaluated all behaviors in young adult (4-5 months) or older (10-11 months) rats to address the persistence of behavioral deficits in adulthood and possible interactions between early ethanol exposure and advancing age. Behavioral deficits in each domain persisted well into adulthood (10-11 months), however, there was no evidence that aging enhances the effects of moderate PAE within the age ranges that were studied.

Rett syndrome and MeCP2

Rett syndrome (RTT) is a severe and progressive neurological disorder, which mainly affects young females. Mutations of the methyl-CpG binding protein 2 (MECP2) gene are the most prevalent cause of classical RTT cases. MECP2 mutations or altered expression are also associated with a spectrum of neurodevelopmental disorders such as autism spectrum disorders with recent links to fetal alcohol spectrum disorders. Collectively, MeCP2 relation to these neurodevelopmental disorders highlights the importance of understanding the molecular mechanisms by which MeCP2 impacts brain development, mental conditions, and compromised brain function. Since MECP2 mutations were discovered to be the primary cause of RTT, a significant progress has been made in the MeCP2 research, with respect to the expression, function and regulation of MeCP2 in the brain and its contribution in RTT pathogenesis. To date, there have been intensive efforts in designing effective therapeutic strategies for RTT benefiting from mouse models and cells collected from RTT patients. Despite significant progress in MeCP2 research over the last few decades, there is still a knowledge gap between the in vitro and in vivo research findings and translating these findings into effective therapeutic interventions in human RTT patients. In this review, we will provide a synopsis of Rett syndrome as a severe neurological disorder and will discuss the role of MeCP2 in RTT pathophysiology.

Brain region-specific expression of MeCP2 isoforms correlates with DNA methylation within Mecp2 regulatory elements

MeCP2 is a critical epigenetic regulator in brain and its abnormal expression or compromised function leads to a spectrum of neurological disorders including Rett Syndrome and autism. Altered expression of the two MeCP2 isoforms, MeCP2E1 and MeCP2E2 has been implicated in neurological complications. However, expression, regulation and functions of the two isoforms are largely uncharacterized. Previously, we showed the role of MeCP2E1 in neuronal maturation and reported MeCP2E1 as the major protein isoform in the adult mouse brain, embryonic neurons and astrocytes. Recently, we showed that DNA methylation at the regulatory elements (REs) within the Mecp2 promoter and intron 1 impact the expression of Mecp2 isoforms in differentiating neural stem cells. This current study is aimed for a comparative analysis of temporal, regional and cell type-specific expression of MeCP2 isoforms in the developing and adult mouse brain. MeCP2E2 displayed a later expression onset than MeCP2E1 during mouse brain development. In the adult female and male brain hippocampus, both MeCP2 isoforms were detected in neurons, astrocytes and oligodendrocytes. Furthermore, MeCP2E1 expression was relatively uniform in different brain regions (olfactory bulb, striatum, cortex, hippocampus, thalamus, brainstem and cerebellum), whereas MeCP2E2 showed differential enrichment in these brain regions. Both MeCP2 isoforms showed relatively similar distribution in these brain regions, except for cerebellum. Lastly, a preferential correlation was observed between DNA methylation at specific CpG dinucleotides within the REs and Mecp2 isoform-specific expression in these brain regions. Taken together, we show that MeCP2 isoforms display differential expression patterns during brain development and in adult mouse brain regions. DNA methylation patterns at the Mecp2 REs may impact this differential expression of Mecp2/MeCP2 isoforms in brain regions. Our results significantly contribute towards characterizing the expression profiles of Mecp2/MeCP2 isoforms and thereby provide insights on the potential role of MeCP2 isoforms in the developing and adult brain.

MeCP2-Related Diseases and Animal Models

The role of epigenetics in human disease has become an area of increased research interest. Collaborative efforts from scientists and clinicians have led to a better understanding of the molecular mechanisms by which epigenetic regulation is involved in the pathogenesis of many human diseases. Several neurological and non-neurological disorders are associated with mutations in genes that encode for epigenetic factors. One of the most studied proteins that impacts human disease and is associated with deregulation of epigenetic processes is Methyl CpG binding protein 2 (MeCP2). MeCP2 is an epigenetic regulator that modulates gene expression by translating epigenetic DNA methylation marks into appropriate cellular responses. In order to highlight the importance of epigenetics to development and disease, we will discuss how MeCP2 emerges as a key epigenetic player in human neurodevelopmental, neurological, and non-neurological disorders. We will review our current knowledge on MeCP2-related diseases, including Rett Syndrome, Angelman Syndrome, Fetal Alcohol Spectrum Disorder, Hirschsprung disease, and Cancer. Additionally, we will briefly discuss about the existing MeCP2 animal models that have been generated for a better understanding of how MeCP2 impacts certain human diseases.

Intergenerational effects of prenatal ethanol on glucose tolerance and insulin response

Consequences of prenatal exposure to ethanol (E) include morphological, physiological, and cognitive deficits and are collectively classified as fetal alcohol spectrum disorders. Adult prenatal E exposed offspring show insulin resistance, and given that in utero hyperglycemic environment can cause metabolic disorders in subsequent generations; we investigated the effects of grandmaternal E on functional glucose and insulin responses of the second generation. Sprague-Dawley (S) rat dams, mated with S males, received E-containing liquid diet and two different control diets between gestational days 8 and 20. Additionally, because prenatal E-induced behavioral deficits can be reversed by simultaneous thyroxine (T4) treatment, another group of dams received 0.3 mg/l T4 in their E diet. Their first-generation (F1) offspring were mated with control Brown Norway (B) males or females to produce SB and BS F2 progeny. Dams consuming E during pregnancy were hyperglycemic, and their F1 offspring showed insulin resistance in the glucose tolerance test (GTT). However, F2 responses to GTT varied based on the sex of prenatal E-exposed parent. BS F2 females, and both male and female SB F2 progeny, displayed hypoglycemic and hyperinsulinemic GTT response patterns. Although administering T4 to E dams normalized thyroid function of the F1 generation, it did not reverse their prenatal E-induced metabolic dysfunction. In contrast, administration of T4 to the alcohol-consuming grandmother reversed or alleviated the aberrant GTT responses of the F2 progeny. Prenatal E-induced dysregulation of glucose metabolism can affect the next generation, possibly via ethanol effects on the germline of the F1 fetus.