Objective Gene expression changes have been reported in the brains of suicide completers. More recently, differences in promoter DNA methylation between suicide completers and comparison subjects in specific genes have been associated with these changes in gene expression patterns, implicating DNA methylation alterations as a plausible component of the pathophysiology of suicide. The authors used a genome-wide approach to investigate the extent of DNA methylation alterations in the brains of suicide completers. Method Promoter DNA methylation was profiled using methylated DNA immunoprecipitation (MeDIP) followed by microarray hybridization in hippocampal tissue from 62 men (46 suicide completers and 16 comparison subjects). The correlation between promoter methylation and expression was investigated by comparing the MeDIP data with gene expression profiles generated through mRNA microarray. Methylation differences between groups were validated on neuronal and nonneuronal DNA fractions isolated by fluorescence-assisted cell sorting. Results The authors identified 366 promoters that were differentially methylated in suicide completers relative to comparison subjects (273 hypermethylated and 93 hypomethylated). Overall, promoter methylation differences were inversely correlated with gene expression differences. Functional annotation analyses revealed an enrichment of differential methylation in the promoters of genes involved, among other functions, in cognitive processes. Validation was performed on the top genes from this category, and these differences were found to occur mainly in the neuronal cell fraction. Conclusions These results suggest broad reprogramming of promoter DNA methylation patterns in the hippocampus of suicide completers. This may help explain gene expression alterations associated with suicide and possibly behavioral changes increasing suicide risk.
Psychiatric disorders are complex multifactorial disorders involving chronic alterations in neural circuit structure and function. While genetic factors play a role in the etiology of disorders such as depression, addiction, and schizophrenia, relatively high rates of discordance among identical twins clearly point to the importance of additional factors. Environmental factors, such as stress, play a major role in the psychiatric disorders by inducing stable changes in gene expression, neural circuit function, and ultimately behavior. Insults at the developmental stage and in adulthood appear to induce distinct maladaptations. Increasing evidence indicates that these sustained abnormalities are maintained by epigenetic modifications in specific brain regions. Indeed, transcriptional dysregulation and associated aberrant epigenetic regulation is a unifying theme in psychiatric disorders. Aspects of depression can be modeled in animals by inducing disease-like states through environmental manipulations, and these studies can provide a more general understanding of epigenetic mechanisms in psychiatric disorders. Understanding how environmental factors recruit the epigenetic machinery in animal models is providing new insights into disease mechanisms in humans. Los trastornos psíquíátricos son complejas enfermedades multífactoriales que íncluyen alteracíones crónicas en la estructura y funcíón de los círcuitos neurales. Aunque los factores genéticos juegan un papel en la etíología de trastornos como la depresíón, las adicciones y la esquizofrenia, las frecuencías relativamente altas de díscordancia entre gemelos ídéntícos apuntan claramente a la importancia de otros factores. Los factores ambientales, como el estrés, juegan un ímportante papel en los trastornos psíquíátricos al inducír cambíos estables en la expresíón géníca, en la funcíón de los circuítos neurales y fínalmente en la conducta. Lesíones en la etapa del desarrollo y en la adultez parece que inducen dístíntas malas adaptacíones. Hay creciente evídencía que índica que estas persistentes anormalídades se mantienen por modíficacíones epigenétícas en regiones cerebrales específicas. Ciertamente, la falta de regulacíón en la transcrípcíón y la regulacíón epígenética aberrante asociada son temas comunes en los trastornos psíquíátricos. Algunos aspectos de la depresíón se pueden modelar en anímales al inducir estados que simulan la enfermedad mediante manipulaciones ambientales; y estos estudios pueden aportar una comprensión más general de los mecanismos epígeneticos en los trastornos psíquíátricos. La comprensíón de cómo los factores ambientales reclutan la maquínaría epigenética en los modelos animales está aportando nuevas perspectivas en los mecanísmos del enfermar en humanos.Les troubles psychiatriques sont complexes et multifactoriels et ils sont associés à des modifications chroniques dans la structure et la fonction des circuits neuronaux. Les facteurs génétiques jouent un rôle dans l'étiologie des troubles comme la dépression, l'addiction et la schizophrénie, mais des taux relativement élevés de discordance parmi les vrais jumeaux indiquent clairement l'importance de facteurs supplémentaires. Des facteurs environnementaux, comme le stress, jouent un rôle majeur dans les troubles psychiatriques en provoquant des modifications stables de l'expression des gènes, de la fonction des circuits neuronaux et enfin du comportement. Des lésions au cours du développement ou à l'âge adulte peuvent entraîner des inadaptations particulières. Selon des données de plus en plus nombreuses, ces anomalies prolongées sont maintenues par des modifications épigénétiques dans des régions cérébrales spécifiques. En effet, la dysrégulation transcriptionnelle et la régulation épigénétique aberrante associée sont un thème commun des troubles psychiatriques. Certains aspects de la dépression peuvent être modélisés chez les animaux en induisant des états mimant la maladie grâce à des manipulations environnementales. Ces études permettent une compréhension plus générale des mécanismes épigénétiques dans les troubles psychiatriques. Connaître la façon dont les facteurs environnementaux recrutent la machinerie épigénétique dans les modèles animaux apporte une nouvelle perspective des mécanismes pathologiques chez l'homme.
Abstract Isolation of cell populations is untangling complex biological interactions, but studies comparing methodologies lack in vivo complexity and draw limited conclusions about the types of transcripts identified by each technique. Furthermore, few studies compare FACS-based techniques to ribosomal affinity purification, and none do so genome-wide. We addressed this gap by systematically comparing nuclear-FACS, whole cell-FACS, and RiboTag affinity purification in the context of D1 or D2 dopamine receptor-expressing medium spiny neuron (MSN) subtypes of the nucleus accumbens (NAc), a key brain reward region. We find that nuclear-FACS-seq generates a substantially longer list of differentially expressed genes between these cell types, and a significantly larger number of neuropsychiatric GWAS hits than the other two methods. RiboTag-seq has much lower coverage of the transcriptome than the other methods, but very efficiently distinguishes D1- and D2-MSNs. We also demonstrate differences between D1- and D2-MSNs with respect to RNA localization, suggesting fundamental cell type differences in mechanisms of transcriptional regulation and subcellular transport of RNAs. Together, these findings guide the field in selecting the RNAseq method that best suits the scientific questions under investigation.
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The lateral habenula (LHb) has emerged as a pivotal brain region implicated in depression, displaying hyperactivity in human and animal models of depression. While the role of LHb efferents in depressive disorders has been acknowledged, the specific synaptic alterations remain elusive. Here, employing optogenetics, retrograde tracing, and ex vivo whole-cell patch-clamp techniques, we investigated synaptic transmission in male mice subjected to chronic social defeat stress (CSDS) at three major LHb neuronal outputs: the dorsal raphe nucleus (DRN), the ventral tegmental area (VTA), and the rostromedial tegmental nucleus (RMTg). Our findings uncovered distinct synaptic adaptations in LHb efferent circuits in response to CSDS. Specifically, CSDS induced in susceptible mice postsynaptic potentiation and postsynaptic depression at the DRN and VTA neurons, respectively, receiving excitatory inputs from the LHb, while CSDS altered presynaptic transmission at the LHb terminals in RMTg in both susceptible and resilient mice. Moreover, whole-cell recordings at projection-defined LHb neurons indicate decreased spontaneous activity in VTA-projecting LHb neurons, accompanied by an imbalance in excitatory–inhibitory inputs at the RMTg-projecting LHb neurons. Collectively, these novel findings underscore the circuit-specific alterations in LHb efferents following chronic social stress, shedding light on potential synaptic adaptations underlying stress-induced depressive-like states.
Melatonin (MLT) and serotonin (5-HT) are two biosynthetically related compounds implicated in several common physiological functions and the etiology of mood disorders. How they interact, though, is not yet fully understood. In this study, single-unit extracellular recordings were used to monitor dorsal raphe nucleus (DR) 5-HT neuronal activity in anesthetized rats, under basal conditions (CTRL), in response to MLT administration, and after pinealectomy (PX) across the light–dark cycle. Under basal conditions, the number of spontaneously active 5-HT neurons and their firing rate were both significantly lower in the dark phase. In the light phase, administration of MLT at low doses (0.5–1 mg/kg, i.v.) decreased 5-HT firing activity. This inhibitory effect of MLT was completely blocked by the MT 1 /MT 2 receptor antagonist luzindole, but not by the selective MT 2 receptor antagonist 4P-PDOT, the selective 5-HT 1A receptor antagonist WAY100635, or by the α 2 adrenoceptor antagonist idazoxan. In the opposite experiment, PX increased 5-HT firing activity in the dark phase, and this was reversed by MLT administration (1 mg/kg, i.v.). Finally, in a forced swim test, MLT (1 mg/kg, i.p.) increased immobility time and decreased swimming behavior. Together, these results suggest that nocturnal MLT secretion imposes tonic inhibitory control over a sub-population of DR 5-HT neurons. This MLT-induced decrease in 5-HT neurotransmission may represent a biological mechanism underlying mood disorders characterized by increased MLT secretion, such as seasonal affective disorder.
