Transcriptional regulation of the hypocretin/orexin gene by NR6A1

Orexin Reserve: A Mechanistic Framework for the Role of Orexins (Hypocretins) in Addiction

In 2014, we proposed that orexin signaling transformed motivationally relevant states into adaptive behavior directed toward exploiting an opportunity or managing a threat, a process we referred to as motivational activation. Advancements in animal models since then have permitted higher-resolution measurements of motivational states; in particular, the behavioral economics approach for studying drug demand characterizes conditions that lead to the enhanced motivation that underlies addiction. This motivational plasticity is paralleled by persistently increased orexin expression in a topographically specific manner-a finding confirmed across species, including in humans. Normalization of orexin levels also reduces drug motivation in addiction models. These new advancements lead us to update our proposed framework for the orexin function. We now propose that the capacity of orexin neurons to exhibit dynamic shifts in peptide production contributes to their role in adaptive motivational regulation and that this is achieved via a pool of reserve orexin neurons. This reserve is normally bidirectionally recruited to permit motivational plasticity that promotes flexible, adaptive behavior. In pathological states such as addiction, however, we propose that the orexin system loses capacity to adaptively adjust peptide production, resulting in focused hypermotivation for drug, driven by aberrantly and persistently high expression in the orexin reserve pool. This mechanistic framework has implications for the understanding and treatment of several psychiatric disorders beyond addiction, particularly those characterized by motivational dysfunction.

Transcriptional regulation of LGALS9 by HAND2 and FOXO1 in human endometrial stromal cells in women with regular cycles

Uterine natural killer cells are regulated via surface inhibitory receptors for IL15 and galectin-9 (LGALS9) secreted by endometrial stromal cells (ESCs). However, the mechanism that regulates LGALS9 mRNA levels in ESCs is unclear. The aim of this study is to clarify the transcriptional regulation of LGALS9 in ESCs. Here, LGALS9 mRNA expression levels significantly decreased in the endometrial tissue in the early- to mid-secretory phase, and recovered in the mid- to late-secretory phase, compared to that in the proliferative phase. In ESCs, LGALS9 mRNA expression significantly decreased following estradiol + medroxyprogesterone acetate treatment for 1 day and increased after 12 days compared to that in the control. The transcriptional activity of the LGALS9 upstream region was upregulated by heart and neural crest derivatives expressed 2 (HAND2) and downregulated by forkhead box O1 (FOXO1). In ESCs, HAND2 expression significantly increased throughout the 12 days treatment with steroid hormones, whereas FOXO1 expression significantly increased on Day 1, reached a plateau, and significantly increased again after 6 days of treatment. Levels of FOXO1 phosphorylation (pFOXO1) remained unchanged after a 3-day treatment of ESCs with steroid hormones, but significantly increased following a 12-day treatment. pFOXO1 could not bind to the DNA and was thus unable to directly suppress LGALS9 transcription. Therefore, expression level of HAND2 and phosphorylation status of FOXO1 may determine LGALS9 mRNA expression. This study provides a novel molecular mechanism underlying the transcriptional regulation of LGALS9 mRNA in ESCs, which could be valuable in the treatment of diseases associated with decidualization failure.

The transcription factor HAND2 up-regulates transcription of the IL15 gene in human endometrial stromal cells

Cyclic changes of the human endometrium, such as proliferation, secretion, and decidualization, occur during regular menstrual cycles. Heart- and neural crest derivatives-expressed transcript 2 (HAND2) is a key transcription factor in progestin-induced decidualization of human endometrial stromal cells (ESCs). It has been suggested that HAND2 regulates interleukin 15 (IL15), a key immune factor required for the activation and survival of uterine natural killer (uNK) cells. Activated uNK cells can promote spiral artery remodeling and secrete cytokines to induce immunotolerance. To date, no studies have evaluated the transcription factors that regulate IL15 expression in human ESCs. In the present study, we examined whether HAND2 controls IL15 transcriptional regulation in human ESCs. Quantitative RT-PCR and histological analyses revealed that HAND2 and IL15 levels increase considerably in the secretory phase of human endometrium tissues. Results from ChIP-quantitative PCR suggested that HAND2 binds to a putative HAND2 motif, which we identified in the upstream region of the human IL15 gene through in silico analysis. Using a luciferase reporter assay, we found that the upstream region of the human IL15 gene up-regulates reporter gene activities in response to estradiol and a progestin representative (medroxyprogesterone) in ESCs. The upstream region of the human IL15 gene also exhibited increasing responsiveness to transfection with a HAND2 expression vector. Of note, deletion and substitution variants of the putative HAND2 motif in the upstream region of IL15 did not respond to HAND2 transfection. These findings confirm that HAND2 directly up-regulates human IL15 transcription in ESCs.

Involvement of PLAGL1/ZAC1 in hypocretin/orexin transcription

The hypocretin/orexin neuropeptide system coordinates the regulation of various physiological processes. Our previous study reported that a reduction in the expression of pleomorphic adenoma gene-like 1 (Plagl1), which encodes a C2H2 zinc-finger transcription factor, occurs in hypocretin neuron-ablated transgenic mice, suggesting that PLAGL1 is co-expressed in hypocretin neurons and regulates hypocretin transcription. The present study examined whether canonical prepro-hypocretin transcription is functionally modulated by PLAGL1. Double immunostaining indicated that the majority of hypocretin neurons were positive for PLAGL1 immunore-activity in the nucleus. Notably, PLAGL1 immunoreactivity in hypocretin neurons was altered in response to several conditions affecting hypocretin function. An uneven localization of PLAGL1 was detected in the nuclei of hypocretin neurons following sleep deprivation. Chromatin immunoprecipitation revealed that endogenous PLAGL1 may bind to a putative PLAGL1-binding site in the proximal region of the hypocretin gene, in the murine hypothalamus. In addition, electroporation of the PLAGL1 expression vector into the fetal hypothalamus promoted hypothalamic hypocretin transcription. These results suggested that PLAGL1 may regulate hypothalamic hypocretin transcription.

DEC2 modulates orexin expression and regulates sleep

Adequate sleep is essential for physical and mental health. We previously identified a missense mutation in the human DEC2 gene (BHLHE41) leading to the familial natural short sleep behavioral trait. DEC2 is a transcription factor regulating the circadian clock in mammals, although its role in sleep regulation has been unclear. Here we report that prepro-orexin, also known as hypocretin (Hcrt), gene expression is increased in the mouse model expressing the mutant hDEC2 transgene (hDEC2-P384R). Prepro-orexin encodes a precursor protein of a neuropeptide producing orexin A and B (hcrt1 and hcrt2), which is enriched in the hypothalamus and regulates maintenance of arousal. In cell culture, DEC2 suppressed prepro-orexin promoter-luc (ore-luc) expression through cis-acting E-box elements. The mutant DEC2 has less repressor activity than WT-DEC2, resulting in increased orexin expression. DEC2-binding affinity for the prepro-orexin gene promoter is decreased by the P384R mutation, likely due to weakened interaction with other transcription factors. In vivo, the decreased immobility time of the mutant transgenic mice is attenuated by an orexin receptor antagonist. Our results suggested that DEC2 regulates sleep/wake duration, at least in part, by modulating the neuropeptide hormone orexin.

Reactivation of hyperglycemia-induced hypocretin (HCRT) gene silencing by N-acetyl-d-mannosamine in the orexin neurons derived from human iPS cells

Orexin neurons regulate critical brain activities for controlling sleep, eating, emotions, and metabolism, and impaired orexin neuron function results in several neurologic disorders. Therefore, restoring normal orexin function and understanding the mechanisms of loss or impairment of orexin neurons represent important goals. As a step toward that end, we generated human orexin neurons from induced pluripotent stem cells (hiPSCs) by treatment with N-acetyl-d-mannosamine (ManNAc) and its derivatives. The generation of orexin neurons was associated with DNA hypomethylation, histone H3/H4 hyperacetylation, and hypo-O-GlcNAcylation on the HCRT gene locus, and, thereby, the treatment of inhibitors of SIRT1 and OGT were effective at inducing orexin neurons from hiPSCs. The prolonged exposure of orexin neurons to high glucose in culture caused irreversible silencing of the HCRT gene, which was characterized by H3/H4 hypoacetylation and hyper-O-GlcNAcylation. The DNA hypomethylation status, once established in orexin neurogenesis, was maintained in the HCRT-silenced orexin neurons, indicating that histone modifications, but not DNA methylation, were responsible for the HCRT silencing. Thus, the epigenetic status of the HCRT gene is unique to the hyperglycemia-induced silencing. Intriguingly, treatment of ManNAc and its derivatives reactivated HCRT gene expression, while inhibitors SIRT1 and the OGT did not. The present study revealed that the HCRT gene was silenced by the hyperglycemia condition, and ManNAc and its derivatives were useful for restoring the orexin neurons.

Modular organization of a hypocretin gene minimal promoter

Orexins or hypocretins are neurotransmitters produced by a small population of neurons in the lateral hypothalamus. This family of peptides modulates sleep-wake cycle, arousal and feeding behaviors; however, the mechanisms regulating their expression remain to be fully elucidated. There is an interest in defining the key molecular elements in orexin regulation, as these may serve to identify targets for generating novel therapies for sleep disorders, obesity and addiction. Our previous studies showed that the expression of orexin was decreased in mice carrying null-mutations of the transcription factor early B-cell factor 2 (ebf2) and that the promoter region of the prepro-orexin (Hcrt) gene contained two putative ebf-binding sites, termed olf-1 sites. In the present study, a minimal promoter region of the murine Hcrt gene was identified, which was able to drive the expression of a luciferase reporter gene in the human 293 cell line. Deletion of the olf1-site proximal to the transcription start site of the Hcrt gene increased reporter gene expression, whereas deletion of the distal olf1-like site decreased its expression. The lentiviral transduction of murine transcription factor ebf2 cDNA into 293 cells increased the gene expression driven by this minimal Hcrt-gene promoter and an electrophoretic mobility shift assays demonstrated that the distal olf1-like sequence was a binding site for ebf2.

Exposure to PM2.5 causes genetic changes in fetal rat cerebral cortex and hippocampus

PM_2.5 travels along the respiratory tract and enters systemic blood circulation. Studies have shown that PM_2.5 increases the incidence of various diseases not only in adults but also in newborn infants. It causes chronic inflammation in pregnant women and retards fetal development. In this study, pregnant rats were exposed to PM_2.5 for extended periods of time and it was found that PM_2.5 exposure increased immune cells in mother rats. In addition, cytokines and free radicals rapidly accumulated in the amniotic fluid and indirectly affected the fetuses. The authors collected cerebral cortex and hippocampus samples at E18 and analyzed changes of miRNA levels. Expression levels of cortical miR-6315, miR-3588, and miR-466b-5p were upregulated, and positively correlated with the genes Pkn2 (astrocyte migration), Gorab (neuritogenesis), and Mobp (allergic encephalomyelitis). In contrast, PM_2.5 decreased expression of miR-338-5p and let-7e-5p, both related to mental development. Further, PM_2.5 exposure increased miR-3560 and let-7b-5p in the hippocampus, two proteins that regulate genes Oxct1 and Lin28b that control ketogenesis and glycosylation, and neural cell differentiation, respectively. miR-99b-5p, miR-92b-5p, and miR-99a-5p were decreased, leading to reduced expression of Kbtbd8 and Adam11 which reduced cell mitosis, migration, and differentiation, and inhibited learning abilities and motor coordination of the fetus. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1412-1425, 2017.

Hypocretin/orexin loss changes the hypothalamic immune response

Hypocretin, also known as orexin, maintains the vigilance state and regulates various physiological processes, such as arousal, sleep, food intake, energy expenditure, and reward. Previously, we found that when wild-type mice and hypocretin/ataxin-3 littermates (which are depleted of hypothalamic hypocretin-expressing neurons postnatally) were administered lipopolysaccharide (LPS), the two genotypes exhibited significant differences in their sleep/wake cycle, including differences in the degree of increase in sleep periods and in recovery from sickness behaviour. In the present study, we examined changes in the hypothalamic vigilance system and in the hypothalamic expression of inflammatory factors in response to LPS in hypocretin/ataxin-3 mice. Peripheral immune challenge with LPS affected the hypothalamic immune response and vigilance states. This response was altered by the loss of hypocretin. Hypocretin expression was inhibited after LPS injection in both hypocretin/ataxin-3 mice and their wild-type littermates, but expression was completely abolished only in hypocretin/ataxin-3 mice. Increases in the number of histidine decarboxylase (HDC)-positive cells and in Hdc mRNA expression were found in hypocretin/ataxin-3 mice, and this increase was suppressed by LPS. Hypocretin loss did not impact the change in expression of hypothalamic inflammatory factors in response to LPS, except for interferon gamma and colony stimulating factor 3. The number of c-Fos-positive/HDC-positive cells in hypocretin/ataxin-3 mice administered LPS injections was elevated, even during the rest period, in all areas, suggesting that there is an increase in the activity of histaminergic neurons in hypocretin/ataxin-3 mice following LPS injection. Taken together, our results suggest a novel role for hypocretin in the hypothalamic response to peripheral immune challenge. Our findings contribute to the understanding of the pathophysiology of narcolepsy.

Hypocretin neuron-specific transcriptome profiling identifies the sleep modulator Kcnh4a

Sleep has been conserved throughout evolution; however, the molecular and neuronal mechanisms of sleep are largely unknown. The hypothalamic hypocretin/orexin (Hcrt) neurons regulate sleep\wake states, feeding, stress, and reward. To elucidate the mechanism that enables these various functions and to identify sleep regulators, we combined fluorescence cell sorting and RNA-seq in hcrt:EGFP zebrafish. Dozens of Hcrt-neuron–specific transcripts were identified and comprehensive high-resolution imaging revealed gene-specific localization in all or subsets of Hcrt neurons. Clusters of Hcrt-neuron–specific genes are predicted to be regulated by shared transcription factors. These findings show that Hcrt neurons are heterogeneous and that integrative molecular mechanisms orchestrate their diverse functions. The voltage-gated potassium channel Kcnh4a, which is expressed in all Hcrt neurons, was silenced by the CRISPR-mediated gene inactivation system. The mutant kcnh4a (kcnh4a^-/-) larvae showed reduced sleep time and consolidation, specifically during the night, suggesting that Kcnh4a regulates sleep.

DOI:http://dx.doi.org/10.7554/eLife.08638.001

Sleep appears to be essential for all animals. The loss of a type of brain cell called the Hypocretin/Orexin (Hcrt) neurons causes the sleep disorder narcolepsy, which disturbs sleep patterns. These neurons also control several other fundamental behaviors and activities, including eating and processing rewards, but it is not clear how Hcrt neurons are able to influence multiple behaviors.

The development and activity of a cell depends to a large extent on the genes it expresses. Yelin-Bekerman et al. have now used genetic techniques to identify a set of genes that are specifically expressed in the Hcrt neurons of zebrafish. Some of these genes are expressed in all of the Hcrt neurons, and some are only expressed in certain subsets of them. Computational methods also revealed a set of “transcription factor” proteins that regulate the expression of clusters of these genes.

Yelin-Bekerman et al. focused on a gene called kcnh4a, and found that this encodes an ion channel protein that allows potassium ions to exit the neurons and stop neuronal activity (this activity is also known as an “action potential”). This gene is expressed in all Hcrt neurons. Further experiments showed that zebrafish that lack the potassium channel sleep less during the night. This therefore suggests that the potassium channel is important for regulating sleep.

Future studies of the genes that are enriched in Hcrt neurons could uncover the mechanisms that enable the neurons to play a role in such a diverse range of processes, including feeding and sleep-wake cycles. These studies should enhance our understanding of the role of sleep and may help to develop treatments for metabolic and sleep disorders.

DOI:http://dx.doi.org/10.7554/eLife.08638.002

Genetic manipulation of the mouse developing hypothalamus through in utero electroporation

Genetic modification of specific regions of the developing mammalian brain is a very powerful experimental approach. However, generating novel mouse mutants is often frustratingly slow. It has been shown that access to the mouse brain developing in utero with reasonable post-operatory survival is possible. Still, results with this procedure have been reported almost exclusively for the most superficial and easily accessible part of the developing brain, i.e. the cortex. The thalamus, a narrower and more medial region, has proven more difficult to target. Transfection into deeper nuclei, especially those of the hypothalamus, is perhaps the most challenging and therefore very few results have been reported. Here we demonstrate a procedure to target the entire hypothalamic neuroepithelium or part of it (hypothalamic regions) for transfection through electroporation. The keys to our approach are longer narcosis times, injection in the third ventricle, and appropriate kind and positioning of the electrodes. Additionally, we show results of targeting and subsequent histological analysis of the most recessed hypothalamic nucleus, the mammillary body.

Epigenetic switching by the metabolism-sensing factors in the generation of orexin neurons from mouse embryonic stem cells

The orexin system plays a central role in the integration of sleep/wake and feeding behaviors in a broad spectrum of neural-metabolic physiology. Orexin-A and orexin-B are produced by the cleavage of prepro-orexin, which is encoded on the Hcrt gene. To date, methods for generating other peptide neurons could not induce orexin neurons from pluripotent stem cells. Considering that the metabolic status affects orexin expression, we supplemented the culture medium with a nutrient factor, ManNAc, and succeeded in generating functional orexin neurons from mouse ES cells. Because DNA methylation inhibitors and histone deacetylase inhibitors could induce Hcrt expression in mouse ES cells, the epigenetic mechanism may be involved in this orexin neurogenesis. DNA methylation analysis showed the presence of a tissue-dependent differentially methylated region (T-DMR) around the transcription start site of the Hcrt gene. In the orexin neurons induced by supplementation of ManNAc, the T-DMR of the Hcrt gene was hypomethylated in association with higher H3/H4 acetylation. Concomitantly, the histone acetyltransferases p300, CREB-binding protein (CBP), and Mgea5 (also called O-GlcNAcase) were localized to the T-DMR in the orexin neurons. In non-orexin-expressing cells, H3/H4 hypoacetylation and hyper-O-GlcNAc modification were observed at the T-DMRs occupied by O-GlcNAc transferase and Sirt1. Therefore, the results of the present study suggest that the glucose metabolite, ManNAc, induces switching from the inactive state by Ogt-Sirt1 to the active state by Mgea5, p300, and CBP at the Hcrt gene locus.

Transcriptional regulation of the hypocretin/orexin gene

The hypocretin (also known as orexin) system reacts to environmental changes in the internal milieu (pH, glucose, and various hormones) and the external environment (activity, fasting, and sleep deprivation) and regulates various physiological functions. Several feedback mechanisms, such as those listed above, have been reported to regulate the hypocretin system even at the transcriptional level. In addition, some transcription factors, such as forkhead box A2; nuclear receptor subfamily 6, group A, member 1; and early B-cell factor 2, were determined to be regulators of the preprohypocretin gene. However, little is known concerning the specific components that react to environmental changes and the determinants of spatial expression of the hypocretin gene within the lateral hypothalamus. This review focuses on the recent findings of transcription factors that regulate preprohypocretin transcription in addition to discussing the future prospects for transcriptional regulation of the hypocretin gene.

Gene network analyses of first service conception in Brangus heifers: use of genome and trait associations, hypothalamic-transcriptome information, and transcription factors

Measures of heifer fertility are economically relevant traits for beef production systems and knowledge of candidate genes could be incorporated into future genomic selection strategies. Ten traits related to growth and fertility were measured in 890 Brangus heifers (3/8 Brahman × 5/8 Angus, from 67 sires). These traits were: BW and hip height adjusted to 205 and 365 d of age, postweaning ADG, yearling assessment of carcass traits (i.e., back fat thickness, intramuscular fat, and LM area), as well as heifer pregnancy and first service conception (FSC). These fertility traits were collected from controlled breeding seasons initiated with estrous synchronization and AI targeting heifers to calve by 24 mo of age. The BovineSNP50 BeadChip was used to ascertain 53,692 SNP genotypes for ∼802 heifers. Associations of genotypes and phenotypes were performed and SNP effects were estimated for each trait. Minimally associated SNP (P < 0.05) and their effects across the 10 traits formed the basis for an association weight matrix and its derived gene network related to FSC (57.3% success and heritability = 0.06 ± 0.05). These analyses yielded 1,555 important SNP, which inferred genes linked by 113,873 correlations within a network. Specifically, 1,386 SNP were nodes and the 5,132 strongest correlations (|r| ≥ 0.90) were edges. The network was filtered with genes queried from a transcriptome resource created from deep sequencing of RNA (i.e., RNA-Seq) from the hypothalamus of a prepubertal and a postpubertal Brangus heifer. The remaining hypothalamic-influenced network contained 978 genes connected by 2,560 edges or predicted gene interactions. This hypothalamic gene network was enriched with genes involved in axon guidance, which is a pathway known to influence pulsatile release of LHRH. There were 5 transcription factors with 21 or more connections: ZMAT3, STAT6, RFX4, PLAGL1, and NR6A1 for FSC. The SNP that identified these genes were intragenic and were on chromosomes 1, 5, 9, and 11. Chromosome 5 harbored both STAT6 and RFX4. The large number of interactions and genes observed with network analyses of multiple sources of genomic data (i.e., GWAS and RNA-Seq) support the concept of FSC being a polygenic trait.

Circadian rhythms and sleep--the metabolic connection

The circadian system coordinates mammalian physiology and behavior with the environmental light-dark cycle. It allocates sleep to the inactivity phase using various mechanisms involving neurotransmitters, nuclear receptors, and protein kinases. These pathways are related to metabolism, indicating that the circadian system and sleep are connected via metabolic parameters. This suggests that organs other than the brain may "sleep." A hypothetic view on this aspect is presented providing a different perspective on sleep regulation.