Gadd45b is an epigenetic regulator of juvenile social behavior and alters local pro-inflammatory cytokine production in the rodent amygdala

Growth arrest and DNA damage-inducible 45: a new player on inflammatory diseases

Growth arrest and DNA damage-inducible 45 (GADD45) proteins are critical stress sensors rapidly induced in response to genotoxic/physiological stress and regulate many cellular functions. Even though the primary function of the proteins is to block the cell cycle, inhibit cell proliferation, promote cell apoptosis, and repair DNA damage to cope with the damage caused by internal and external stress on the body, evidence has shown that GADD45 also has the function to modulate innate and adaptive immunity and plays a broader role in inflammatory and autoimmune diseases. In this review, we focus on the immunomodulatory role of GADD45 in inflammatory and autoimmune diseases. First, we describe the regulatory factors that affect the expression of GADD45. Then, we introduce its immunoregulatory roles on immune cells and the critical signaling pathways mediated by GADD45. Finally, we discuss its immunomodulatory effects in various inflammatory and autoimmune diseases.

Retrotransposons and the brain: Exploring a complex relationship between mobile elements, stress, and neurological health

Environmental experiences during early life, including stress, can significantly impact brain development and behavior. Early life stress (ELS) is linked to an increased risk for various psychiatric disorders including anxiety, depression, and substance use disorders. Epigenetic mechanisms have increasingly been of interest to understand how environmental factors contribute to reprogramming the brain and alter risk and resilience to developing psychiatric disorders. However, we know very little about mobile elements or the regulation of mobile elements and their contribution to psychiatric disorders. Recently, advances in genomics have contributed to our understanding of mobile elements, including the retrotransposon LINE-1 (L1) and their potential role in mediating environmental experiences. Yet we still do not understand how these elements may contribute to psychiatric disorders. Future research leveraging cutting-edge technologies will deepen our understanding of these mobile elements. By elucidating their role in development and how stress may impact them, we may unlock new avenues for therapeutic and diagnostic innovations.

Brain, behavior, and physiological changes associated with predator stress-An animal model for trauma exposure in adult and neonatal rats

The use of predators and predator odor as stressors is an important and ecologically relevant model for studying the impact of behavioral responses to threat. Here we summarize neural substrates and behavioral changes in rats resulting from predator exposure. We briefly define the impact predator exposure has on neural targets throughout development (neonatal, juvenile, and adulthood). These findings allow us to conceptualize the impact of predator exposure in the brain, which in turn may have broader implications for human disorders such as PTSD. Importantly, inclusion of sex as a biological variable yields distinct results that may indicate neural substrates impacted by predator exposure differ based on sex.

Advances in the role of the GADD45 family in neurodevelopmental, neurodegenerative, and neuropsychiatric disorders

The growth arrest and DNA damage inducible protein 45 (GADD45) family comprises stress-induced nuclear proteins that interact with DNA demethylases to facilitate DNA demethylation, thereby regulating diverse cellular processes including oxidative stress, DNA damage repair, apoptosis, proliferation, differentiation, inflammation, and neuroplasticity by modulating the expression patterns of specific genes. Widely expressed in the central nervous system, the GADD45 family plays a pivotal role in various neurological disorders, rendering it a potential therapeutic target for central nervous system diseases. This review presented a comprehensive overview of the expression patterns and potential mechanisms of action associated with each member of GADD45 family (GADD45α, GADD45β, and GADD45γ) in neurodevelopmental, neurodegenerative, and neuropsychiatric disorders, while also explored strategies to harness these mechanisms for intervention and treatment. Future research should prioritize the development of effective modulators targeting the GADD45 family for clinical trials aimed at treating central nervous system diseases.

The impact of social defeat on basomedial amygdala neuronal activity in adult male rats

Social stressors negatively impact social function, and this is mediated by the amygdala across species. Social defeat stress is an ethologically relevant social stressor in adult male rats that increases social avoidance, anhedonia, and anxiety-like behaviors. While amygdala manipulations can mitigate the negative effects of social stressors, the impact of social defeat on the basomedial subregion of the amygdala is relatively unclear. Understanding the role of the basomedial amygdala may be especially important, as prior work has demonstrated that it drives physiological responses to stress, including heart-rate related responses to social novelty. In the present study, we quantified the impact of social defeat on social behavior and basomedial amygdala neuronal responses using anesthetized in vivo extracellular electrophysiology. Socially defeated rats displayed increased social avoidance behavior towards novel Sprague Dawley conspecifics and reduced time initiating social interactions relative to controls. This effect was most pronounced in rats that displayed defensive, boxing behavior during social defeat sessions. We next found that socially defeated rats showed lower overall basomedial amygdala firing and altered the distribution of neuronal responses relative to the control condition. We separated neurons into low and high Hz firing groups, and neuronal firing was reduced in both low and high Hz groups but in a slightly different manner. This work demonstrates that basomedial amygdala activity is sensitive to social stress, displaying a distinct pattern of social stress-driven activity relative to other amygdala subregions.

Methylation and expression of glucocorticoid receptor exon-1 variants and FKBP5 in teenage suicide-completers

A dysregulated hypothalamic-pituitary-adrenal (HPA) axis has repeatedly been demonstrated to play a fundamental role in psychiatric disorders and suicide, yet the mechanisms underlying this dysregulation are not clear. Decreased expression of the glucocorticoid receptor (GR) gene, which is also susceptible to epigenetic modulation, is a strong indicator of impaired HPA axis control. In the context of teenage suicide-completers, we have systematically analyzed the 5'UTR of the GR gene to determine the expression levels of all GR exon-1 transcript variants and their epigenetic state. We also measured the expression and the epigenetic state of the FK506-binding protein 51 (FKBP5/FKBP51), an important modulator of GR activity. Furthermore, steady-state DNA methylation levels depend upon the interplay between enzymes that promote DNA methylation and demethylation activities, thus we analyzed DNA methyltransferases (DNMTs), ten-eleven translocation enzymes (TETs), and growth arrest- and DNA-damage-inducible proteins (GADD45). Focusing on both the prefrontal cortex (PFC) and hippocampus, our results show decreased expression in specific GR exon-1 variants and a strong correlation of DNA methylation changes with gene expression in the PFC. FKBP5 expression is also increased in both areas suggesting a decreased GR sensitivity to cortisol binding. We also identified aberrant expression of DNA methylating and demethylating enzymes in both brain regions. These findings enhance our understanding of the complex transcriptional regulation of GR, providing evidence of epigenetically mediated reprogramming of the GR gene, which could lead to possible epigenetic influences that result in lasting modifications underlying an individual's overall HPA axis response and resilience to stress.

The role of Gadd45b in neurologic and neuropsychiatric disorders: An overview

Growth arrest and DNA damage-inducible beta (Gadd45b) is directly intertwined with stress-induced DNA repair, cell cycle arrest, survival, and apoptosis. Previous research on Gadd45b has focused chiefly on non-neuronal cells. Gadd45b is extensively expressed in the nervous system and plays a critical role in epigenetic DNA demethylation, neuroplasticity, and neuroprotection, according to accumulating evidence. This article provided an overview of the preclinical and clinical effects of Gadd45b, as well as its hypothesized mechanisms of action, focusing on major psychosis, depression, autism, stroke, seizure, dementia, Parkinson’s disease, and autoimmune diseases of the nervous system.

Under or Absent Reporting of Light Stimuli in Testing of Anxiety-Like Behaviors in Rodents: The Need for Standardization

Behavioral neuroscience tests such as the Light/Dark Test, the Open Field Test, the Elevated Plus Maze Test, and the Three Chamber Social Interaction Test have become both essential and widely used behavioral tests for transgenic and pre-clinical models for drug screening and testing. However, as fast as the field has evolved and the contemporaneous involvement of technology, little assessment of the literature has been done to ensure that these behavioral neuroscience tests that are crucial to pre-clinical testing have well-controlled ethological motivation by the use of lighting (i.e., Lux). In the present review paper, N = 420 manuscripts were examined from 2015 to 2019 as a sample set (i.e., n = ~20–22 publications per year) and it was found that only a meager n = 50 publications (i.e., 11.9% of the publications sampled) met the criteria for proper anxiogenic and anxiolytic Lux reported. These findings illustrate a serious concern that behavioral neuroscience papers are not being vetted properly at the journal review level and are being released into the literature and public domain making it difficult to assess the quality of the science being reported. This creates a real need for standardizing the use of Lux in all publications on behavioral neuroscience techniques within the field to ensure that contributions are meaningful, avoid unnecessary duplication, and ultimately would serve to create a more efficient process within the pre-clinical screening/testing for drugs that serve as anxiolytic compounds that would prove more useful than what prior decades of work have produced. It is suggested that improving the standardization of the use and reporting of Lux in behavioral neuroscience tests and the standardization of peer-review processes overseeing the proper documentation of these methodological approaches in manuscripts could serve to advance pre-clinical testing for effective anxiolytic drugs. This report serves to highlight this concern and proposes strategies to proactively remedy them as the field moves forward for decades to come.

Single-Cell Sequencing Analysis of the db/db Mouse Hippocampus Reveals Cell-Type-Specific Insights Into the Pathobiology of Diabetes-Associated Cognitive Dysfunction

Diabetes-associated cognitive decline (DCD), is one of the complications of diabetes, which is characterized by a series of neurophysiological and pathological abnormalities. However, the exact pathogenesis of DCD is still unknown. Single-cell RNA sequencing (scRNA-seq) could discover unusual subpopulations, explore functional heterogeneity and identify signaling pathways and potential markers. The aim of this research was to provide deeper opinion into molecular and cellular changes underlying DCD, identify different cellular types of the diabetic mice hippocampus at single-cell level, and elucidate the factors mediating the pathogenesis of DCD. To elucidate cell specific gene expression changes in the hippocampus of diabetic encephalopathy. Single-cell RNA sequencing of hippocampus from db/m and db/db mice was carried out. Subclustering analysis was performed to further describe microglial cell subpopulations. Interestingly using immunohistochemistry, these findings were confirmed at the protein level. Single cell analysis yielded transcriptome data for 14621 hippocampal cells and defined 11 different cell types. Analysis of differentially expressed genes in the microglia compartments indicated that infection- and immune system process- associated terms, oxidative stress and inflammation play vital roles in the progression of DCD. Compared with db/m mouse, experiments at the protein level supported the activation of microglia, increased expression of inflammatory factors and oxidative stress damage in the hippocampus of db/db mouse. In addition, a major finding of our research was the subpopulation of microglia that express genes related to pro-inflammatory disease-associated microglia (DAM). Our research reveals pathological alterations of inflammation and oxidative stress mediated hippocampal damage in the db/db mice, and may provide potential diagnostic biomarkers and therapeutic interventions for DCD.

Gadd45b is a novel mediator of depression-like behaviors and neuroinflammation after cerebral ischemia

BACKGROUND

Poststroke depression (PSD) is an important consequence after stroke, with a negative impact on stroke outcome. Recent evidence points to a modulatory role of Growth arrest and DNA-damage-inducible protein 45 beta (Gadd45b) in depression. Herein, we evaluated the antidepressant efficacy and mechanism underlying the potent therapeutic effects of Gadd45b after cerebral ischemia.

METHODS

Adult male Sprague-Dawley rats were subjected to cerebral ischemia by permanent middle cerebral artery occlusion (MCAO). The sucrose preference test (SPT), forced swim test (FST), and tail suspension test (TST) were performed after completing MCAO to study the antidepressant-like effects. The expression of brain-derived neurotrophic factor (BDNF) and neuroinflammation were determined in the hippocampus.

RESULTS

We showed that Gadd45b knockdown induced depression-like behaviors after cerebral ischemia, including increased immobility time in the FST and TST and reduced sucrose preference. Gadd45b knockdown enhanced the expression of pro-inflammatory cytokines IL-6 and TNF-α, accompanying with decreased protein levels of BDNF in the hippocampus. Moreover, the levels of phosphorylated ERK and CREB, which have been implicated in events downstream of BDNF signaling, were also decreased after cerebral ischemia.

CONCLUSION

Hence, the results showed that Gadd45b is a promising drug candidate for treating PSD and possibly other nervous system diseases associated with neuroinflammation. Gadd45b may have therapeutic potential for PSD through BDNF-ERK-CREB pathway and neuroinflammation.

Early life stress during the neonatal period alters social play and Line1 during the juvenile stage of development

Early life stress (ELS) has been shown to have a significant impact on typical brain development and the manifestation of psychological disorders through epigenetic modifications that alter gene expression. Line1, a retrotransposon associated with genetic diversity, has been linked with various psychological disorders that are associated with ELS. Our previous work demonstrated altered Line1 DNA copy number in the neonatal period following stressful experiences; we therefore chose to investigate whether early life stress altered Line1 retrotransposition persists into the juvenile period of development. Our study uses a neonatal predator odor exposure (POE) paradigm to model ELS in rats. We examined Line1 using qPCR to assess Line1 expression levels and DNA copy number in the male and female juvenile amygdala, hippocampus and prefrontal cortex-areas chosen for their association with affective disorders and stress. We report a sex difference in Line1 levels within the juvenile amygdala. We also find that ELS significantly increases Line1 DNA copy number within the juvenile amygdala which correlates with reduced juvenile social play levels, suggesting the possibility that Line1 may influence juvenile social development.

GADD45B Facilitates Metastasis of Ovarian Cancer Through Epithelial-Mesenchymal Transition

Background

Growth arrest and DNA-damage-inducible 45 beta (GADD45B) is overexpressed and is associated with poor clinical outcomes in many human cancers, but the clinical implication of GADD45B in epithelial ovarian cancer (EOC) remains unclear.

Methods

Bioinformatics analysis of The Cancer Genome Atlas (TCGA) and gene expression omnibus (GEO) cohorts was used to illustrate the relationship between GADD45B expression and metastasis, as well as the survival time of EOC. GADD45B was downregulated by siRNAs in EOC cells, and migration ability was determined by a transwell assay and wound-healing assay. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis and gene set enrichment analysis (GSEA) were conducted to discover the downstream pathway of GADD45B. The regulation of epithelial–mesenchymal transition (EMT) by GADD45B was verified by Western blotting and qRT-PCR. Finally, the correlation of GADD45B expression with EOC metastasis was investigated in EOC tissues by immunohistochemistry.

Results

Overexpression of GADD45B indicates shorter overall survival time and progression-free survival time, and it is an independent risk factor for poor survival in EOC patients. Elevated GADD45B is related to venous invasion, lymphatic invasion and peritoneal carcinomatosis. Downregulation of GADD45B decreases the migration of ES2 and SKOV3 cells. Further KEGG enrichment analysis and GSEA revealed that EMT may be the downstream pathway of GADD45B. In addition, reduced GADD45B increases the expression of E-cadherin and decreases that of N-cadherin and vimentin. Finally, immunohistochemical analysis of GADD45B expression revealed that the expression of GADD45B in omental metastatic tissues was higher than that in matched primary ovarian cancer tissues. These results suggest that elevated GADD45B promotes the motility of ovarian cancer cells through EMT and is associated with EOC metastasis.

Conclusion

GADD45B can promote the motility of ovarian cancer cells through EMT, is associated with EOC metastasis, and may be a new biomarker of metastasis and prognosis.

Neonatal Tactile Stimulation Alters Behaviors in Heterozygous Serotonin Transporter Male Rats: Role of the Amygdala

The serotonin transporter (SERT) gene, especially the short allele of the human serotonin transporter linked polymorphic region (5-HTTLPR), has been associated with the development of stress-related neuropsychiatric disorders. In line, exposure to early life stress in SERT knockout animals contributes to anxiety- and depression-like behavior. However, there is a lack of investigation of how early-life exposure to beneficial stimuli, such as tactile stimulation (TS), affects later life behavior in these animals. In this study, we investigated the effect of TS on social, anxiety, and anhedonic behavior in heterozygous SERT knockouts rats and wild-type controls and its impact on gene expression in the basolateral amygdala. Heterozygous SERT^+/– rats were submitted to TS during postnatal days 8–14, for 10 min per day. In adulthood, rats were assessed for social and affective behavior. Besides, brain-derived neurotrophic factor (Bdnf) gene expression and its isoforms, components of glutamatergic and GABAergic systems as well as glucocorticoid-responsive genes were measured in the basolateral amygdala. We found that exposure to neonatal TS improved social and affective behavior in SERT^+/– animals compared to naïve SERT^+/– animals and was normalized to the level of naïve SERT^+/+ animals. At the molecular level, we observed that TS per se affected Bdnf, the glucocorticoid-responsive genes Nr4a1, Gadd45β, the co-chaperone Fkbp5 as well as glutamatergic and GABAergic gene expression markers including the enzyme Gad67, the vesicular GABA transporter, and the vesicular glutamate transporter genes. Our results suggest that exposure of SERT^+/– rats to neonatal TS can normalize their phenotype in adulthood and that TS per se alters the expression of plasticity and stress-related genes in the basolateral amygdala. These findings demonstrate the potential effect of a supportive stimulus in SERT rodents, which are more susceptible to develop psychiatric disorders.

Norepinephrine, neurodevelopment and behavior

Neurotransmitters play critical roles in the developing nervous system. Among the neurotransmitters, norepinephrine (NE) is in particular postulated to be an important regulator of brain development. NE is expressed during early stages of development and is known to regulate both the development of noradrenergic neurons and the development of target areas. NE participates in the shaping and the wiring of the nervous system during the critical periods of development, and perturbations in this process can alter the brain's developmental trajectory, which in turn can cause long-lasting and even permanent changes in the brain function and behavior later in life. Here we will briefly review evidence for the role of noradrenergic system in neurodevelopmental processes and will discuss about the potential disruptors of noradrenergic system during development and their behavioral consequences.

Memory and neuromodulation: A perspective of DNA methylation

Neuromodulation techniques have shown promising efficacy on memory function and understanding the epigenetic mechanisms contributing to these processes would shed light on the molecular outcomes essential for cognition. In this review, we highlight some epigenetic mechanisms underlying neuromodulation and regulatory effects of neuronal activity-induced DNA methylation on genes that are highly involved in memory formation. Next, we examine the evidence to support DNA methyltransferase 3a, methyl-CpG binding protein 2, and DNA demethylase as possible memory modulation targets. Finally, we report the recent developments in the field of neuromodulation and explore the potential of these techniques for future neuroepigenetic research.

Inflammatory domains modulate autism spectrum disorder susceptibility during maternal nutritional programming

Autism spectrum disorder (ASD) is a complex neurodevelopmental disease which involves functional and structural defects in selective central nervous system (CNS) regions harming capability to process and respond to external stimuli. In addition to genetic background, etiological causes of ASD have not been fully clarified. Maternal immune activation (MIA) during pregnancy have been proposed as a potential etiological cause leading to aberrant synaptic pruning and microglia-mediated neurogenesis impairment. Several clinical studies suggest that pro-inflammatory profile during maternal obesity associates with a higher risk of having a child with autism. In this context, the effect of maternal programing by high fat diet overconsumption during pregnancy sets a pro-inflammatory profile partly dependent on an epigenetic program of immunity which promotes brain micro and macrostructural abnormalities in the offspring that might last through adulthood accompanied by phenotypic changes in ASD subjects. Of note, maternal programming of inflammation during development seems to integrate the CNS and peripheral immune system cross-talk which arrays central inflammatory domains coordinating ASD behavior. In this review, we discuss basic and clinical studies regarding the effects of obesity-induced MIA on peripheral immune cells and microglia priming and their relationship with brain structural alterations in ASD models. Also, we show supportive evidence stating the role of maternal programming on epigenetic gene activation in immune cells of ASD subjects. We suggest that maternal programming by hypercaloric diets during development sets a central and peripheral immune cross-talk which potentially might modulate brain macro and microstructural defects leading to autism susceptibility.

Gadd45b mediates depressive-like role through DNA demethylation

Animal studies using chronic social defeat stress (CSDS) in mice showed that brain-derived neurotrophic factor (BDNF) signaling in the mesolimbic dopamine (DA) circuit is important for the development of social aversion. However, the downstream molecular targets after BDNF release from ventral tegmental area (VTA) DA terminals are unknown. Here, we show that depressive-like behaviors induced by CSDS are mediated in part by Gadd45b downstream of BDNF signaling in the nucleus accumbens (NAc). We show that Gadd45b mRNA levels are increased in susceptible but not resilient mice. Intra-NAc infusion of BDNF or optical stimulation of VTA DA terminals in NAc enhanced Gadd45b expression levels in the NAc. Importantly, Gadd45b downregulation reversed social avoidance in susceptible mice. Together, these data suggest that Gadd45b in NAc contributes to susceptibility to social stress. In addition, we investigated the function of Gadd45b in demethylating CpG islands of representative gene targets, which have been associated with a depressive phenotype in humans and animal models. We found that Gadd45b downregulation changes DNA methylation levels in a phenotype-, gene-, and locus-specific fashion. Together, these results highlight the contribution of Gadd45b and changes in DNA methylation in mediating the effects of social stress in the mesolimbic DA circuit.

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.

Vocal practice regulates singing activity-dependent genes underlying age-independent vocal learning in songbirds

The development of highly complex vocal skill, like human language and bird songs, is underlain by learning. Vocal learning, even when occurring in adulthood, is thought to largely depend on a sensitive/critical period during postnatal development, and learned vocal patterns emerge gradually as the long-term consequence of vocal practice during this critical period. In this scenario, it is presumed that the effect of vocal practice is thus mainly limited by the intrinsic timing of age-dependent maturation factors that close the critical period and reduce neural plasticity. However, an alternative, as-yet untested hypothesis is that vocal practice itself, independently of age, regulates vocal learning plasticity. Here, we explicitly discriminate between the influences of age and vocal practice using a songbird model system. We prevented zebra finches from singing during the critical period of sensorimotor learning by reversible postural manipulation. This enabled to us to separate lifelong vocal experience from the effects of age. The singing-prevented birds produced juvenile-like immature song and retained sufficient ability to acquire a tutored song even at adulthood when allowed to sing freely. Genome-wide gene expression network analysis revealed that this adult vocal plasticity was accompanied by an intense induction of singing activity-dependent genes, similar to that observed in juvenile birds, rather than of age-dependent genes. The transcriptional changes of activity-dependent genes occurred in the vocal motor robust nucleus of the arcopallium (RA) projection neurons that play a critical role in the production of song phonology. These gene expression changes were accompanied by neuroanatomical changes: dendritic spine pruning in RA projection neurons. These results show that self-motivated practice itself changes the expression dynamics of activity-dependent genes associated with vocal learning plasticity and that this process is not tightly linked to age-dependent maturational factors.

How is plasticity associated with vocal learning regulated during a critical period? Although there are abundant studies on the critical period in sensory systems, which are passively regulated by the external environment, few studies have manipulated the sensorimotor experience through the entire critical period. Thus, it is a commonly held belief that age or intrinsic maturation is a crucial factor for the closure of the critical period of vocal learning. Contrary to this idea, our study using songbirds provides a new insight that self-motivated vocal practice, not age, regulates vocal learning plasticity during the critical period. To examine the effects of vocal practice on vocal learning, we prevented juvenile zebra finches from singing during the critical period by postural manipulation, which separated the contribution of lifelong vocal experience from that of age. When these birds were allowed to freely sing as adults, they generated highly plastic songs and maintained the ability to mimic tutored songs, as normal juveniles did. Genome-wide transcriptome analysis revealed that both juveniles and singing-prevented adults, but not normally reared adults, expressed a similar set of singing-dependent genes in a song nucleus in the brain that regulates syllable acoustics. However, age-dependent genes were still similarly expressed in both singing-prevented and normally reared adult birds. These results exhibit that vocal learning plasticity is actively controlled by self-motivated vocal practice.

Maternal Deprivation Enhances Contextual Fear Memory via Epigenetically Programming Second-Hit Stress-Induced Reelin Expression in Adult Rats

BACKGROUND

Early-life stress increases the risk for posttraumatic stress disorder. However, the epigenetic mechanism of early-life stress-induced susceptibility to posttraumatic stress disorder in adulthood remains unclear.

METHODS

Rat pups were exposed to maternal deprivation during postnatal days 1 to 14 for 3 hours daily and treated with the DNA methyltransferase inhibitor zebularine, L-methionine, or vehicle 7 days before contextual fear conditioning, which was used as a second stress and to mimic the reexperiencing symptom of posttraumatic stress disorder in adulthood. Long-term potentiation, dendritic spine density, DNA methyltransferase mRNA, Reelin gene methylation, and Reelin protein expression in the hippocampal CA1 were measured.

RESULTS

Maternal deprivation enhanced contextual fear memory in adulthood. Meanwhile, maternal deprivation decreased DNA methyltransferase mRNA and Reelin gene methylation in the hippocampal CA1 on postnatal days 22 and 90. Reelin protein expression was increased in the hippocampal CA1 following contextual fear conditioning in adulthood. Furthermore, compared with rats that experienced maternal deprivation alone, rats also exposed to contextual fear conditioning showed an enhanced induction of hippocampal long-term potentiation and increased dendritic spine density in the hippocampal CA1 following contextual fear conditioning in adulthood. Zebularine pretreatment led to an enhancement of contextual fear memory, hypomethylation of the Reelin gene, and increased Reelin protein expression in adult rats, while L-methionine had the opposite effects.

CONCLUSIONS

Maternal deprivation can epigenetically program second-hit stress-induced Reelin expression and enhance the susceptibility to contextual fear memory in adulthood. These findings provide a new framework for understanding the cumulative stress hypothesis.

The Role of Activity-Dependent DNA Demethylation in the Adult Brain and in Neurological Disorders

Over the last decade, an increasing number of reports underscored the importance of epigenetic regulations in brain plasticity. Epigenetic elements such as readers, writers and erasers recognize, establish, and remove the epigenetic tags in nucleosomes, respectively. One such regulation concerns DNA-methylation and demethylation, which are highly dynamic and activity-dependent processes even in the adult neurons. It is nowadays widely believed that external stimuli control the methylation marks on the DNA and that such processes serve transcriptional regulation in neurons. In this mini-review, we cover the current knowledge on the regulatory mechanisms controlling in particular DNA demethylation as well as the possible functional consequences in health and disease.

Neuroprotective effect of acute ethanol intoxication in TBI is associated to the hierarchical modulation of early transcriptional responses

Ethanol intoxication is a risk factor for traumatic brain injury (TBI) but clinical evidence suggests that it may actually improve the prognosis of intoxicated TBI patients. We have employed a closed, weight-drop TBI model of different severity (2cm or 3cm falling height), preceded (-30min) or followed (+20min) by ethanol administration (5g/Kg). This protocol allows us to study the interaction of binge ethanol intoxication in TBI, monitoring behavioral changes, histological responses and the transcriptional regulation of a series of activity-regulated genes (immediate early genes, IEGs). We demonstrate that ethanol pretreatment before moderate TBI (2cm) significantly reduces neurological impairment and accelerates recovery. In addition, better preservation of neuronal numbers and cFos+cells was observed 7days after TBI. At transcriptional level, ethanol reduced the upregulation of a subset of IEGs encoding for transcription factors such as Atf3, c-Fos, FosB, Egr1, Egr3 and Npas4 but did not affect the upregulation of others (e.g. Gadd45b and Gadd45c). While a subset of IEGs encoding for effector proteins (such as Bdnf, InhbA and Dusp5) were downregulated by ethanol, others (such as Il-6) were unaffected. Notably, the majority of genes were sensitive to ethanol only when administered before TBI and not afterwards (the exceptions being c-Fos, Egr1 and Dusp5). Furthermore, while severe TBI (3cm) induced a qualitatively similar (but quantitatively larger) transcriptional response to moderate TBI, it was no longer sensitive to ethanol pretreatment. Thus, we have shown that a subset of the TBI-induced transcriptional responses were sensitive to ethanol intoxication at the instance of trauma (ultimately resulting in beneficial outcomes) and that the effect of ethanol was restricted to a certain time window (pre TBI treatment) and to TBI severity (moderate). This information could be critical for the translational value of ethanol in TBI and for the design of clinical studies aimed at disentangling the role of ethanol intoxication in TBI.

N6-methyladenine is an epigenetic marker of mammalian early life stress

Recent evidence described 6-methyladenine (6 mA) as a novel epigenetic regulator in a variety of multicellular species, including rodents; however, its capacity to influence gene expression in the mammalian brain remains unknown. We examined if 6 mA is present and regulated by early life stress associated with predator odor exposure (POE) within the developing rat amygdala. Our results provide evidence that 6 mA is present in the mammalian brain, is altered within the Htr2a gene promoter by early life stress and biological sex, and increased 6 mA is associated with gene repression. These data suggest that methylation of adenosine within mammalian DNA may be used as an additional epigenetic biomarker for investigating the development of stress-induced neuropathology.

Prenatal bisphenol A (BPA) exposure alters the transcriptome of the neonate rat amygdala in a sex-specific manner: a CLARITY-BPA consortium study

Bisphenol A (BPA) is a widely recognized endocrine disruptor prevalent in many household items. Because experimental and epidemiological data suggest links between prenatal BPA exposure and altered affective behaviors in children, even at levels below the current US FDA No Observed Adverse Effect Level (NOAEL) of 5mg/kg body weight (bw)/day, there is concern that early life exposure may alter neurodevelopment. The current study was conducted as part of the CLARITY-BPA (Consortium Linking Academic and Regulatory Insights on BPA Toxicity) program and examined the full amygdalar transcriptome on postnatal day (PND) 1, with the hypothesis that prenatal BPA exposure would alter the expression of genes and pathways fundamental to sex-specific affective behaviors. NCTR Sprague-Dawley dams were gavaged from gestational day 6 until parturition with BPA (2.5, 25, 250, 2500, or 25000μg/kg bw/day), a reference estrogen (0.05 or 0.5μg ethinyl estradiol (EE₂)/kg bw/day), or vehicle. PND 1 amygdalae were microdissected and gene expression was assessed with qRT-PCR (all exposure groups) and RNAseq (vehicle, 25 and 250μg BPA, and 0.5μg EE₂ groups only). Our results demonstrate that that prenatal BPA exposure can disrupt the transcriptome of the neonate amygdala, at doses below the FDA NOAEL, in a sex-specific manner and indicate that the female amygdala may be more sensitive to BPA exposure during fetal development. We also provide additional evidence that developmental BPA exposure can interfere with estrogen, oxytocin, and vasopressin signaling pathways in the developing brain and alter signaling pathways critical for synaptic organization and transmission.

Perinatal inflammation and adult psychopathology: From preclinical models to humans

Perinatal environment plays a crucial role in brain development and determines its function through life. Epidemiological studies and clinical reports link perinatal exposure to infection and/or immune activation to various psychiatric disorders. In addition, accumulating evidence from animal models shows that perinatal inflammation can affect various behaviors relevant to psychiatric disorders such as schizophrenia, autism, anxiety and depression. Remarkably, the effects on behavior and brain function do not always depend on the type of inflammatory stimulus or the perinatal age targeted, so diverse inflammatory events can have similar consequences on the brain. Moreover, other perinatal environmental factors that affect behavior (e.g. diet and stress) also elicit inflammatory responses. Understanding the interplay between perinatal environment and inflammation on brain development is required to identify the mechanisms through which perinatal inflammation affect brain function in the adult animal. Evidence for the role of the peripheral immune system and glia on perinatal programming of behavior is discussed in this review, along with recent evidence for the role of epigenetic mechanisms affecting gene expression in the brain.

Growth Arrest and DNA-damage–inducible Protein 45β-mediated DNA Demethylation of Voltage-dependent T-type Calcium Channel 3.2 Subunit Enhances Neuropathic Allodynia after Nerve Injury in Rats

Background

Growth arrest and DNA-damage–inducible protein 45β reactivates methylation-silenced neural plasticity-associated genes through DNA demethylation. However, growth arrest and DNA-damage–inducible protein 45β–dependent demethylation contributes to neuropathic allodynia-associated spinal plasticity remains unclear.

Methods

Adult male Sprague–Dawley rats (654 out of 659) received a spinal nerve ligation or a sham operation with or without intrathecal application of one of the following: growth arrest and DNA-damage–inducible protein 45β messenger RNA–targeted small interfering RNA, lentiviral vector expressing growth arrest and DNA-damage–inducible protein 45β, Ro 25–6981 (an NR2B-bearing N-methyl-d-aspartate receptor antagonist), or KN-93 (a calmodulin-dependent protein kinase II antagonist) were used for behavioral measurements, Western blotting, immunofluorescence, dot blots, detection of unmodified cytosine enrichment at cytosine-phosphate-guanine site, chromatin immunoprecipitation quantitative polymerase chain reaction analysis, and slice recordings.

Results

Nerve ligation-enhanced growth arrest and DNA-damage–inducible protein 45β expression (n = 6) in ipsilateral dorsal horn neurons accompanied with behavioral allodynia (n = 7). Focal knockdown of growth arrest and DNA-damage–inducible protein 45β expression attenuated ligation-induced allodynia (n = 7) by reducing the binding of growth arrest and DNA-damage–inducible protein 45β to the voltage-dependent T-type calcium channel 3.2 subunit promoter (n = 6) that decreased expression of and current mediated by the voltage-dependent T-type calcium channel 3.2 subunit (both n = 6). In addition, NR2B-bearing N-methyl-d-aspartate receptors and calmodulin-dependent protein kinase II act in an upstream cascade to increase growth arrest and DNA-damage–inducible protein 45β expression, hence enhancing demethylation at the voltage-dependent T-type calcium channel 3.2 subunit promoter and up-regulating voltage-dependent T-type calcium channel 3.2 subunit expression. Intrathecal administration of Ro 25–6981, KN-93, or a growth arrest and DNA-damage–inducible protein 45β–targeting small interfering RNA (n = 6) reversed the ligation-induced enrichment of unmodified cytosine at the voltage-dependent T-type calcium channel 3.2 subunit promoter by increasing the associated 5-formylcytosine and 5-carboxylcytosine levels.

Conclusions

By converting 5-formylcytosine or 5-carboxylcytosine to unmodified cytosine, the NR2B-bearing N-methyl-d-aspartate receptor, calmodulin-dependent protein kinase II, or growth arrest and DNA-damage–inducible protein 45β pathway facilitates voltage-dependent T-type calcium channel 3.2 subunit gene demethylation to mediate neuropathic allodynia.

Why are behavioral and immune traits linked?

Through behavior, animals interact with a world where parasites abound. It is easy to understand how behavioral traits can thus have a differential effect on pathogen exposure. Harder to understand is why we observe behavioral traits to be linked to immune defense traits. Is variation in immune traits a consequence of behavior-induced variation in immunological experiences? Or is variation in behavioral traits a function of immune capabilities? Is our immune system a much bigger driver of personality than anticipated? In this review, I provide examples of how behavioral and immune traits co-vary. I then explore the different routes linking behavioral and immune traits, emphasizing on the physiological/hormonal mechanisms that could lead to immune control of behavior. Finally, I discuss why we should aim at understanding more about the mechanisms connecting these phenotypic traits.

DNA repair and erasure of 5-methylcytosine in vertebrates

DNA methylation plays important roles in development and disease. Yet, only recently has the dynamic nature of this epigenetic mark via oxidation and DNA repair-mediated demethylation been recognized. A major conceptual challenge to the model that DNA methylation is reversible is the risk of genomic instability, which may come with widespread DNA repair activity. Here, we focus on recent advances in mechanisms of TET-TDG mediated demethylation and cellular strategies that avoid genomic instability. We highlight the recently discovered involvement of NEIL DNA glycosylases, which cooperate with TDG in oxidative demethylation to accelerate substrate turnover and promote the organized handover of harmful repair intermediates to maintain genome stability.

Sex differences in Gadd45b expression and methylation in the developing rodent amygdala

Precise spatiotemporal epigenetic regulation of the genome facilitates species-typical development; sexual differentiation of the brain by gonadal hormones and sex chromosomes causes extensive epigenetic reprogramming of many cells in the body, including the brain, and may indirectly predispose males and females to different psychiatric conditions. We and others have demonstrated sex differences in DNA methylation, as well as in the enzymes that form, or 'write', this epigenetic modification. However, while a growing body of evidence suggests that DNA methylation undergoes rapid turnover and is dynamically regulated in vivo, to our knowledge no studies have been done investigating whether sex differences exist in the epigenetic 'erasers' during postnatal development. Here we report sex differences in the expression of growth arrest and DNA damage inducible factor β (Gadd45b), but not family members α (a) or γ (g), in the neonatal and juvenile rodent amygdala.

Genome-wide alterations in hippocampal 5-hydroxymethylcytosine links plasticity genes to acute stress

Environmental stress is among the most important contributors to increased susceptibility to develop psychiatric disorders, including anxiety and post-traumatic stress disorder. While even acute stress alters gene expression, the molecular mechanisms underlying these changes remain largely unknown. 5-hydroxymethylcytosine (5hmC) is a novel environmentally sensitive DNA modification that is highly enriched in post-mitotic neurons and is associated with active transcription of neuronal genes. Recently, we found a hippocampal increase of 5hmC in the glucocorticoid receptor gene (Nr3c1) following acute stress, warranting a deeper investigation of stress-related 5hmC levels. Here we used an established chemical labeling and affinity purification method coupled with high-throughput sequencing technology to generate the first genome-wide profile of hippocampal 5hmC following exposure to acute restraint stress and a one-hour recovery. This approach found a genome-wide disruption in 5hmC associated with acute stress response, primarily in genic regions, and identified known and potentially novel stress-related targets that have a significant enrichment for neuronal ontological functions. Integration of these data with hippocampal gene expression data from these same mice found stress-related hydroxymethylation correlated to altered transcript levels and sequence motif predictions indicated that 5hmC may function by mediating transcription factor binding to these transcripts. Together, these data reveal an environmental impact on this newly discovered epigenetic mark in the brain and represent a critical step toward understanding stress-related epigenetic mechanisms that alter gene expression and can lead to the development of psychiatric disorders.