A Neural Circuit for Gut-Induced Reward.

The gut is now recognized as a major regulator of motivational and emotional states. However, the relevant gut-brain neuronal circuitry remains unknown. We show that optical activation of gut-innervating vagal sensory neurons recapitulates the hallmark effects of stimulating brain reward neurons. Specifically, right, but not left, vagal sensory ganglion activation sustained self-stimulation behavior, conditioned both flavor and place preferences, and induced dopamine release from Substantia nigra. Cell-specific transneuronal tracing revealed asymmetric ascending pathways of vagal origin throughout the CNS. In particular, transneuronal labeling identified the glutamatergic neurons of the dorsolateral parabrachial region as the obligatory relay linking the right vagal sensory ganglion to dopamine cells in Substantia nigra. Consistently, optical activation of parabrachio-nigral projections replicated the rewarding effects of right vagus excitation. Our findings establish the vagal gut-to-brain axis as an integral component of the neuronal reward pathway. They also suggest novel vagal stimulation approaches to affective disorders.

The 7q11.23 Protein DNAJC30 Interacts with ATP Synthase and Links Mitochondria to Brain Development.

Despite the known causality of copy-number variations (CNVs) to human neurodevelopmental disorders, the mechanisms behind each gene's contribution to the constellation of neural phenotypes remain elusive. Here, we investigated the 7q11.23 CNV, whose hemideletion causes Williams syndrome (WS), and uncovered that mitochondrial dysfunction participates in WS pathogenesis. Dysfunction is facilitated in part by the 7q11.23 protein DNAJC30, which interacts with mitochondrial ATP-synthase machinery. Removal of Dnajc30 in mice resulted in hypofunctional mitochondria, diminished morphological features of neocortical pyramidal neurons, and altered behaviors reminiscent of WS. The mitochondrial features are consistent with our observations of decreased integrity of oxidative phosphorylation supercomplexes and ATP-synthase dimers in WS. Thus, we identify DNAJC30 as an auxiliary component of ATP-synthase machinery and reveal mitochondrial maladies as underlying certain defects in brain development and function associated with WS.

UCP2 Regulates Mitochondrial Fission and Ventromedial Nucleus Control of Glucose Responsiveness.

The ventromedial nucleus of the hypothalamus (VMH) plays a critical role in regulating systemic glucose homeostasis. How neurons in this brain area adapt to the changing metabolic environment to regulate circulating glucose levels is ill defined. Here, we show that glucose load results in mitochondrial fission and reduced reactive oxygen species in VMH neurons mediated by dynamin-related peptide 1 (DRP1) under the control of uncoupling protein 2 (UCP2). Probed by genetic manipulations and chemical-genetic control of VMH neuronal circuitry, we unmasked that this mitochondrial adaptation determines the size of the pool of glucose-excited neurons in the VMH and that this process regulates systemic glucose homeostasis. Thus, our data unmasked a critical cellular biological process controlled by mitochondrial dynamics in VMH regulation of systemic glucose homeostasis.

O-GlcNAc transferase enables AgRP neurons to suppress browning of white fat.

Induction of beige cells causes the browning of white fat and improves energy metabolism. However, the central mechanism that controls adipose tissue browning and its physiological relevance are largely unknown. Here, we demonstrate that fasting and chemical-genetic activation of orexigenic AgRP neurons in the hypothalamus suppress the browning of white fat. O-linked ß-N-acetylglucosamine (O-GlcNAc) modification of cytoplasmic and nuclear proteins regulates fundamental cellular processes. The levels of O-GlcNAc transferase (OGT) and O-GlcNAc modification are enriched in AgRP neurons and are elevated by fasting. Genetic ablation of OGT in AgRP neurons inhibits neuronal excitability through the voltage-dependent potassium channel, promotes white adipose tissue browning, and protects mice against diet-induced obesity and insulin resistance. These data reveal adipose tissue browning as a highly dynamic physiological process under central control, in which O-GlcNAc signaling in AgRP neurons is essential for suppressing thermogenesis to conserve energy in response to fasting.

Mitochondrial dynamics controlled by mitofusins regulate Agrp neuronal activity and diet-induced obesity.

Mitochondria are key organelles in the maintenance of cellular energy metabolism and integrity. Here, we show that mitochondria number decrease but their size increase in orexigenic agouti-related protein (Agrp) neurons during the transition from fasted to fed to overfed state. These fusion-like dynamic changes were cell-type specific, as they occurred in the opposite direction in anorexigenic pro-opiomelanocortin (POMC) neurons. Interfering with mitochondrial fusion mechanisms in Agrp neurons by cell-selectively knocking down mitofusin 1 (Mfn1) or mitofusin 2 (Mfn2) resulted in altered mitochondria size and density in these cells. Deficiency in mitofusins impaired the electric activity of Agrp neurons during high-fat diet (HFD), an event reversed by cell-selective administration of ATP. Agrp-specific Mfn1 or Mfn2 knockout mice gained less weight when fed a HFD due to decreased fat mass. Overall, our data unmask an important role for mitochondrial dynamics governed by Mfn1 and Mfn2 in Agrp neurons in central regulation of whole-body energy metabolism.

A serotonin-dependent mechanism explains the leptin regulation of bone mass, appetite, and energy expenditure.

Leptin inhibition of bone mass accrual requires the integrity of specific hypothalamic neurons but not expression of its receptor on these neurons. The same is true for its regulation of appetite and energy expenditure. This suggests that leptin acts elsewhere in the brain to achieve these three functions. We show here that brainstem-derived serotonin (BDS) favors bone mass accrual following its binding to Htr2c receptors on ventromedial hypothalamic neurons and appetite via Htr1a and 2b receptors on arcuate neurons. Leptin inhibits these functions and increases energy expenditure because it reduces serotonin synthesis and firing of serotonergic neurons. Accordingly, while abrogating BDS synthesis corrects the bone, appetite and energy expenditure phenotypes caused by leptin deficiency, inactivation of the leptin receptor in serotonergic neurons recapitulates them fully. This study modifies the map of leptin signaling in the brain and identifies a molecular basis for the common regulation of bone and energy metabolisms. For a video summary of this article, see the PaperFlick file with the Supplemental Data available online.

AgRP neurons control structure and function of the medial prefrontal cortex.

Hypothalamic agouti-related peptide and neuropeptide Y-expressing (AgRP) neurons have a critical role in both feeding and non-feeding behaviors of newborn, adolescent, and adult mice, suggesting their broad modulatory impact on brain functions. Here we show that constitutive impairment of AgRP neurons or their peripubertal chemogenetic inhibition resulted in both a numerical and functional reduction of neurons in the medial prefrontal cortex (mPFC) of mice. These changes were accompanied by alteration of oscillatory network activity in mPFC, impaired sensorimotor gating, and altered ambulatory behavior that could be reversed by the administration of clozapine, a non-selective dopamine receptor antagonist. The observed AgRP effects are transduced to mPFC in part via dopaminergic neurons in the ventral tegmental area and may also be conveyed by medial thalamic neurons. Our results unmasked a previously unsuspected role for hypothalamic AgRP neurons in control of neuronal pathways that regulate higher-order brain functions during development and in adulthood.

The steroid hormone estriol (E3) regulates epigenetic programming of fetal mouse brain and reproductive tract.

BACKGROUND: Estriol (E3) is a steroid hormone formed only during pregnancy in primates including humans. Although E3 is synthesized at large amounts through a complex pathway involving the fetus and placenta, it is not required for the maintenance of pregnancy and has classically been considered virtually inactive due to associated very weak canonical estrogen signaling. However, estrogen exposure during pregnancy may have an effect on organs both within and outside the reproductive system, and compounds with binding affinity for estrogen receptors weaker than E3 have been found to impact reproductive organs and the brain. Here, we explore potential effects of E3 on fetal development using mouse as a model system. RESULTS: We administered E3 to pregnant mice, exposing the fetus to E3. Adult females exposed to E3 in utero (E3-mice) had increased fertility and superior pregnancy outcomes. Female and male E3-mice showed decreased anxiety and increased exploratory behavior. The expression levels and DNA methylation patterns of multiple genes in the uteri and brains of E3-mice were distinct from controls. E3 promoted complexing of estrogen receptors with several DNA/histone modifiers and their binding to target genes. E3 functions by driving epigenetic change, mediated through epigenetic modifier interactions with estrogen receptors rather than through canonical nuclear transcriptional activation. CONCLUSIONS: We identify an unexpected functional role for E3 in fetal reproductive system and brain. We further identify a novel mechanism of estrogen action, through recruitment of epigenetic modifiers to estrogen receptors and their target genes, which is not correlated with the traditional view of estrogen potency.

Endometriosis alters brain electrophysiology, gene expression and increases pain sensitization, anxiety, and depression in female mice.

Endometriosis is an estrogen-dependent inflammatory disorder among reproductive-aged women associated with pelvic pain, anxiety, and depression. Pain is characterized by central sensitization; however, it is not clear if endometriosis leads to increased pain perception or if women with the disease are more sensitive to pain, increasing the detection of endometriosis. Endometriosis was induced in mice and changes in behavior including pain perception, brain electrophysiology, and gene expression were characterized. Behavioral tests revealed that mice with endometriosis were more depressed, anxious and sensitive to pain compared to sham controls. Microarray analyses confirmed by qPCR identified differential gene expression in several regions of brain in mice with endometriosis. In these mice, genes such as Gpr88, Glra3 in insula, Chrnb4, Npas4 in the hippocampus, and Lcn2 in the amygdala were upregulated while Lct, Serpina3n (insula), and Nptx2 (amygdala) were downregulated. These genes are involved in anxiety, locomotion, and pain. Patch clamp recordings in the amygdala were altered in endometriosis mice demonstrating an effect of endometriosis on brain electrophysiology. Endometriosis induced pain sensitization, anxiety, and depression by modulating brain gene expression and electrophysiology; the effect of endometriosis on the brain may underlie pain sensitization and mood disorders reported in women with the disease.

UCP2 mediates ghrelin's action on NPY/AgRP neurons by lowering free radicals.

The gut-derived hormone ghrelin exerts its effect on the brain by regulating neuronal activity. Ghrelin-induced feeding behaviour is controlled by arcuate nucleus neurons that co-express neuropeptide Y and agouti-related protein (NPY/AgRP neurons). However, the intracellular mechanisms triggered by ghrelin to alter NPY/AgRP neuronal activity are poorly understood. Here we show that ghrelin initiates robust changes in hypothalamic mitochondrial respiration in mice that are dependent on uncoupling protein 2 (UCP2). Activation of this mitochondrial mechanism is critical for ghrelin-induced mitochondrial proliferation and electric activation of NPY/AgRP neurons, for ghrelin-triggered synaptic plasticity of pro-opiomelanocortin-expressing neurons, and for ghrelin-induced food intake. The UCP2-dependent action of ghrelin on NPY/AgRP neurons is driven by a hypothalamic fatty acid oxidation pathway involving AMPK, CPT1 and free radicals that are scavenged by UCP2. These results reveal a signalling modality connecting mitochondria-mediated effects of G-protein-coupled receptors on neuronal function and associated behaviour.

Prolyl endopeptidase-deficient mice have reduced synaptic spine density in the CA1 region of the hippocampus, impaired LTP, and spatial learning and memory.

Prolyl endopeptidase (PREP) is a phylogenetically conserved serine protease and, in humans and rodents, is highly expressed in the brain. Several neuropeptides associated with learning and memory and neurodegenerative disorders have been proposed to be the substrates for PREP, suggesting a possible role for PREP in these processes. However, its physiological function remains elusive. Combining genetic, anatomical, electrophysiological, and behavioral approaches, we show that PREP genetrap mice have decreased synaptic spine density in the CA1 region of the hippocampus, reduced hippocampal long-term potentiation, impaired hippocampal-mediated learning and memory, and reduced growth-associated protein-43 levels when compared with wild-type controls. These observations reveal a role for PREP in mediating hippocampal plasticity and spatial memory formation, with implications for its pharmacological manipulation in diseases related to cognitive impairment.

Repeated in vivo exposure of cocaine induces long-lasting synaptic plasticity in hypocretin/orexin-producing neurons in the lateral hypothalamus in mice.

Hypocretin (orexin), a neuropeptide synthesized exclusively in the perifornical/lateral hypothalamus, is critical for drug seeking and relapse, but it is not clear how the circuitry centred on hypocretin-producing neurons (hypocretin neurons) is modified by drugs of abuse and how changes in this circuit might alter behaviours related to drug addiction. In this study, we show that repeated, but not single, in vivo cocaine administration leads to a long-lasting, experience-dependent potentiation of glutamatergic synapses on hypocretin neurons in mice following a cocaine-conditioned place preference (CPP) protocol. The synaptic potentiation occurs postsynaptically and probably involves up-regulation of AMPA-type glutamate receptors on hypocretin neurons. Phosphorylation of cAMP response element-binding protein (CREB) is also significantly increased in hypocretin neurons in cocaine-treated animals, suggesting that CREB-mediated pathways may contribute to synaptic potentiation in these cells. Furthermore, the potentiation of synaptic efficacy in hypocretin neurons persists during cocaine withdrawal, but reverses to baseline levels after prolonged abstinence. Finally, the induction of long-term potentiation (LTP) triggered by a high-frequency stimulation is facilitated in hypocretin neurons in cocaine-treated mice, suggesting that long-lasting changes in synapses onto hypocretin neurons would probably be further potentiated by other stimuli (such as concurrent environmental cues) paired with the drug. In summary, we show here that hypocretin neurons undergo experience-dependent synaptic potentiation that is distinct from that reported in other reward systems, such as the ventral tegmental area, following exposure to cocaine. These findings support the idea that the hypocretin system is important for behavioural changes associated with cocaine administration in animals and humans.

A central thermogenic-like mechanism in feeding regulation: an interplay between arcuate nucleus T3 and UCP2.

The active thyroid hormone, triiodothyronine (T3), regulates mitochondrial uncoupling protein activity and related thermogenesis in peripheral tissues. Type 2 deiodinase (DII), an enzyme that catalyzes active thyroid hormone production, and mitochondrial uncoupling protein 2 (UCP2) are also present in the hypothalamic arcuate nucleus, where their interaction and physiological significance have not been explored. Here, we report that DII-producing glial cells are in direct apposition to neurons coexpressing neuropeptide Y (NPY), agouti-related protein (AgRP), and UCP2. Fasting increased DII activity and local thyroid hormone production in the arcuate nucleus in parallel with increased GDP-regulated UCP2-dependent mitochondrial uncoupling. Fasting-induced T3-mediated UCP2 activation resulted in mitochondrial proliferation in NPY/AgRP neurons, an event that was critical for increased excitability of these orexigenic neurons and consequent rebound feeding following food deprivation. These results reveal a physiological role for a thyroid-hormone-regulated mitochondrial uncoupling in hypothalamic neuronal networks.

The prevalence of nonalcoholic fatty liver disease and its association with lifestyle/dietary habits among university faculty and staff in Chengdu.

OBJECTIVE: To investigate the prevalence of nonalcoholic fatty liver disease (NAFLD) in different university categories and its association with lifestyle/dietary habits. METHODS: A cross-sectional study was carried out on 9 378 faculty members and staff who participated in an annual health checkup at three universities selected by random cluster sampling. Demographic, anthropometric, biochemical indices and abdominal ultrasound measurements were collected. A nested case-control study was conducted with 200 NAFLD cases and 200 controls matched by gender, age (±3 years), and university. RESULTS: The overall prevalence of NAFLD was 10.3% (13.7% in males and 6.8% in females). The prevalence was significantly higher in the science and engineering university (22.1%) than in the comprehensive universities with (6.4%) and without (10.9%) medical colleges. Obesity/overweight, hyperlipidemia, diabetes mellitus, and family history of NAFLD were independently associated with higher risk of NAFLD, as were frequent consumption of desserts and salty/spicy foods. Using nutritional supplements was a protective factor against NAFLD. Intake of coarse cereals, potatoes, vegetables, fruits, and milk was significantly lower, and intake of red meat, viscera, candies and pastries, cooking oil, and total energy was significantly higher in participants with NAFLD than in controls. CONCLUSION: Science and engineering university faculty and staff are key targets for NAFLD prevention. NAFLD is closely associated with age, gender, university type, metabolic diseases, and lifestyle/dietary habits.

Ventromedial hypothalamic OGT drives adipose tissue lipolysis and curbs obesity.

The ventromedial hypothalamus (VMH) is known to regulate body weight and counterregulatory response. However, how VMH neurons regulate lipid metabolism and energy balance remains unknown. O-linked ß-d-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation), catalyzed by O-GlcNAc transferase (OGT), is considered a cellular sensor of nutrients and hormones. Here, we report that genetic ablation of OGT in VMH neurons inhibits neuronal excitability. Mice with VMH neuron-specific OGT deletion show rapid weight gain, increased adiposity, and reduced energy expenditure, without significant changes in food intake or physical activity. The obesity phenotype is associated with adipocyte hypertrophy and reduced lipolysis of white adipose tissues. In addition, OGT deletion in VMH neurons down-regulates the sympathetic activity and impairs the sympathetic innervation of white adipose tissues. These findings identify OGT in the VMH as a homeostatic set point that controls body weight and underscore the importance of the VMH in regulating lipid metabolism through white adipose tissue-specific innervation.

UCP2-dependent redox sensing in POMC neurons regulates feeding.

Paradoxically, glucose, the primary driver of satiety, activates a small population of anorexigenic pro-opiomelanocortin (POMC) neurons. Here, we show that lactate levels in the circulation and in the cerebrospinal fluid are elevated in the fed state and the addition of lactate to glucose activates the majority of POMC neurons while increasing cytosolic NADH generation, mitochondrial respiration, and extracellular pyruvate levels. Inhibition of lactate dehydrogenases diminishes mitochondrial respiration, NADH production, and POMC neuronal activity. However, inhibition of the mitochondrial pyruvate carrier has no effect. POMC-specific downregulation of Ucp2 (Ucp2PomcKO), a molecule regulated by fatty acid metabolism and shown to play a role as transporter in the malate-aspartate shuttle, abolishes lactate- and glucose-sensing of POMC neurons. Ucp2PomcKO mice have impaired glucose metabolism and are prone to obesity on a high-fat diet. Altogether, our data show that lactate through redox signaling and blocking mitochondrial glucose utilization activates POMC neurons to regulate feeding and glucose metabolism.

LINE-1 activation in the cerebellum drives ataxia.

Dysregulation of long interspersed nuclear element 1 (LINE-1, L1), a dominant class of transposable elements in the human genome, has been linked to neurodegenerative diseases, but whether elevated L1 expression is sufficient to cause neurodegeneration has not been directly tested. Here, we show that the cerebellar expression of L1 is significantly elevated in ataxia telangiectasia patients and strongly anti-correlated with the expression of epigenetic silencers. To examine the role of L1 in the disease etiology, we developed an approach for direct targeting of the L1 promoter for overexpression in mice. We demonstrated that L1 activation in the cerebellum led to Purkinje cell dysfunctions and degeneration and was sufficient to cause ataxia. Treatment with a nucleoside reverse transcriptase inhibitor blunted ataxia progression by reducing DNA damage, attenuating gliosis, and reversing deficits of molecular regulators for calcium homeostasis in Purkinje cells. Our study provides the first direct evidence that L1 activation can drive neurodegeneration.

TET3 epigenetically controls feeding and stress response behaviors via AGRP neurons.

The TET family of dioxygenases promote DNA demethylation by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). Hypothalamic agouti-related peptide-expressing (AGRP-expressing) neurons play an essential role in driving feeding, while also modulating nonfeeding behaviors. Besides AGRP, these neurons produce neuropeptide Y (NPY) and the neurotransmitter GABA, which act in concert to stimulate food intake and decrease energy expenditure. Notably, AGRP, NPY, and GABA can also elicit anxiolytic effects. Here, we report that in adult mouse AGRP neurons, CRISPR-mediated genetic ablation of Tet3, not previously known to be involved in central control of appetite and metabolism, induced hyperphagia, obesity, and diabetes, in addition to a reduction of stress-like behaviors. TET3 deficiency activated AGRP neurons, simultaneously upregulated the expression of Agrp, Npy, and the vesicular GABA transporter Slc32a1, and impeded leptin signaling. In particular, we uncovered a dynamic association of TET3 with the Agrp promoter in response to leptin signaling, which induced 5hmC modification that was associated with a chromatin-modifying complex leading to transcription inhibition, and this regulation occurred in both the mouse models and human cells. Our results unmasked TET3 as a critical central regulator of appetite and energy metabolism and revealed its unexpected dual role in the control of feeding and other complex behaviors through AGRP neurons.

AgRP neurons control feeding behaviour at cortical synapses via peripherally derived lysophospholipids.

Phospholipid levels are influenced by peripheral metabolism. Within the central nervous system, synaptic phospholipids regulate glutamatergic transmission and cortical excitability. Whether changes in peripheral metabolism affect brain lipid levels and cortical excitability remains unknown. Here, we show that levels of lysophosphatidic acid (LPA) species in the blood and cerebrospinal fluid are elevated after overnight fasting and lead to higher cortical excitability. LPA-related cortical excitability increases fasting-induced hyperphagia, and is decreased following inhibition of LPA synthesis. Mice expressing a human mutation (Prg-1R346T) leading to higher synaptic lipid-mediated cortical excitability display increased fasting-induced hyperphagia. Accordingly, human subjects with this mutation have higher body mass index and prevalence of type 2 diabetes. We further show that the effects of LPA following fasting are under the control of hypothalamic agouti-related peptide (AgRP) neurons. Depletion of AgRP-expressing cells in adult mice decreases fasting-induced elevation of circulating LPAs, as well as cortical excitability, while blunting hyperphagia. These findings reveal a direct influence of circulating LPAs under the control of hypothalamic AgRP neurons on cortical excitability, unmasking an alternative non-neuronal route by which the hypothalamus can exert a robust impact on the cortex and thereby affect food intake.