POMC Neurons: Feeding, Energy Metabolism, and Beyond

KCNB1-Leptin receptor complexes couple electric and endocrine function in the melanocortin neurons of the hypothalamus

The neurons of the melanocortin system regulate feeding and energy homeostasis through a combination of electrical and endocrine mechanisms. However, the molecular basis for this functional heterogeneity is poorly understood. Here, a voltage-gated potassium (Kv+) channel named KCNB1 (alias Kv2.1) forms stable complexes with the leptin receptor (LepR) in a subset of hypothalamic neurons including proopiomelanocortin (POMC) expressing neurons of the Arcuate nucleus (ARHPOMC). Mice lacking functional KCNB1 channels (NULL mice) have less adipose tissue and circulating leptin than WT animals and are insensitive to anorexic stimuli induced by leptin administration. NULL mice produce aberrant amounts of POMC at any developmental stage. Canonical LepR-STAT3 signaling-which underlies POMC production-is impaired, whereas non-canonical insulin receptor substrate PI3K/Akt/FOXO1 and ERK signaling are constitutively upregulated in NULL hypothalami. The levels of proto-oncogene c-Fos-that provides an indirect measure of neuronal activity-are higher in arcuate NULL neurons compared to WT and most importantly do not increase in the former upon leptin stimulation. Hence, a Kv channel provides a molecular link between neuronal excitability and endocrine function in hypothalamic neurons.

Molecular cell types as functional units of the efferent vagus nerve

The vagus nerve vitally connects the brain and body to coordinate digestive, cardiorespiratory, and immune functions. Its efferent neurons, which project their axons from the brainstem to the viscera, are thought to comprise "functional units" - neuron populations dedicated to the control of specific vagal reflexes or organ functions. Previous research indicates that these functional units differ from one another anatomically, neurochemically, and physiologically but have yet to define their identity in an experimentally tractable way. However, recent work with genetic technology and single-cell genomics suggests that genetically distinct subtypes of neurons may be the functional units of the efferent vagus. Here we review how these approaches are revealing the organizational principles of the efferent vagus in unprecedented detail.

Hypothalamic POMC neuron-specific knockout of MC4R affects insulin sensitivity by regulating Kir2.1

BACKGROUND

Imbalance in energy regulation is a major cause of insulin resistance and diabetes. Melanocortin-4 receptor (MC4R) signaling at specific sites in the central nervous system has synergistic but non-overlapping functions. However, the mechanism by which MC4R in the arcuate nucleus (ARC) region regulates energy balance and insulin resistance remains unclear.

METHODS

The MC4Rflox/flox mice with proopiomelanocortin (POMC) -Cre mice were crossed to generate the POMC-MC4Rflox/+ mice. Then POMC-MC4Rflox/+ mice were further mated with MC4Rflox/flox mice to generate the POMC-MC4Rflox/flox mice in which MC4R is selectively deleted in POMC neurons. Bilateral injections of 200 nl of AAV-sh-Kir2.1 (AAV-sh-NC was used as control) were made into the ARC of the hypothalamus. Oxygen consumption, carbon dioxide production, respiratory exchange ratio and energy expenditure were measured by using the CLAMS; Total, visceral and subcutaneous fat was analyzed using micro-CT. Co-immunoprecipitation assays (Co-IP) were used to analyze the interaction between MC4R and Kir2.1 in GT1-7 cells.

RESULTS

POMC neuron-specific ablation of MC4R in the ARC region promoted food intake, impaired energy expenditure, leading to increased weight gain and impaired systemic glucose homeostasis. Additionally, MC4R ablation reduced the activation of POMC neuron, and is not tissue-specific for peripheral regulation, suggesting the importance of its central regulation. Mechanistically, sequencing analysis and Co-IP assay demonstrated a direct interaction of MC4R with Kir2.1. Knockdown of Kir2.1 in POMC neuron-specific ablation of MC4R restored the effect of MC4R ablation on energy expenditure and systemic glucose homeostasis, indicating by reduced body weight and ameliorated insulin resistance.

CONCLUSION

Hypothalamic POMC neuron-specific knockout of MC4R affects energy balance and insulin sensitivity by regulating Kir2.1. Kir2.1 represents a new target and pathway that could be targeted in obesity.

Polymorphisms in corticotrophin-releasing hormone-proopiomalanocortin (CRH-POMC) system genes: Neuroimmune contributions to psoriasis disease

BACKGROUND

Skin is a target organ and source of the corticotropin-releasing hormone-proopiomelanocortin (CRH-POMC) system, operating as a coordinator and executor of responses to stress. Environmental stress exacerbates and triggers inflammatory skin diseases through modifying the cellular components of the immune system supporting the importance of CRH-POMC system in the pathogenesis of psoriasis. The aim of this study was to analyse the association of CRH-POMC polymorphisms with psoriasis and evaluate transcript expression of lesional psoriatic and normal skin in RNA-seq data.

METHODS

Samples of 104 patients with psoriasis and 174 healthy controls were genotyped for 42 single nucleotide polymorphisms (SNPs) of CRH-POMC using Applied Biosystems SNPlex™ method. The transcript quantification was performed using Salmon software v1.3.0.

RESULTS

This study demonstrated the associations between melanocortin 1 receptor (MC1R) polymorphisms rs2228479, rs3212369, dopachrome tautomerase (DCT) polymorphisms rs7987802, rs2031526, rs9524501 and psoriasis in the Tatar population. Very strong association was evident for the SNP rs7987802 in the DCT gene (pc  = 5.95е-006) in psoriasis patients. Additionally, the haplotype analysis provided AT DCT (rs7992630 and rs7987802) and AGA MC1R (rs3212358, 2228479 and 885479) haplotypes significantly associated (pc  ˂ 0.05) with psoriasis in the Tatar population, supporting the involvement of DCT and MC1R to the psoriasis susceptibility. Moreover, MC1R-203 and DCT-201 expression levels were decreased in psoriasis lesional skin compared with healthy control skin.

CONCLUSIONS

This study is the first to identify genetic variants of the MC1R and DCT genes significantly associated with psoriasis in Tatar population. Our results support potential roles of CRH-POMC system genes and DCT in the pathogenesis of psoriasis.

The Bidirectional Relationship of NPY and Mitochondria in Energy Balance Regulation

Energy balance is regulated by several hormones and peptides, and neuropeptide Y is one of the most crucial in feeding and energy expenditure control. NPY is regulated by a series of peripheral nervous and humoral signals that are responsive to nutrient sensing, but its role in the energy balance is also intricately related to the energetic status, namely mitochondrial function. During fasting, mitochondrial dynamics and activity are activated in orexigenic neurons, increasing the levels of neuropeptide Y. By acting on the sympathetic nervous system, neuropeptide Y modulates thermogenesis and lipolysis, while in the peripheral sites, it triggers adipogenesis and lipogenesis instead. Moreover, both central and peripheral neuropeptide Y reduces mitochondrial activity by decreasing oxidative phosphorylation proteins and other mediators important to the uptake of fatty acids into the mitochondrial matrix, inhibiting lipid oxidation and energy expenditure. Dysregulation of the neuropeptide Y system, as occurs in metabolic diseases like obesity, may lead to mitochondrial dysfunction and, consequently, to oxidative stress and to the white adipose tissue inflammatory environment, contributing to the development of a metabolically unhealthy profile. This review focuses on the interconnection between mitochondrial function and dynamics with central and peripheral neuropeptide Y actions and discusses possible therapeutical modulations of the neuropeptide Y system as an anti-obesity tool.

Lipopolysaccharide-induced immune stress negatively regulates broiler chicken growth via the COX-2-PGE2-EP4 signaling pathway

Aims

Immune stress in broiler chickens is characterized by the development of persistent pro-inflammatory responses that contribute to degradation of production performance. However, the underlying mechanisms that cause growth inhibition of broilers with immune stress are not well defined.

Methods

A total of 252 1-day-old Arbor Acres(AA) broilers were randomly allocated to three groups with six replicates per group and 14 broilers per replicate. The three groups comprised a saline control group, an Lipopolysaccharide (LPS) (immune stress) group, and an LPS and celecoxib group corresponding to an immune stress group treated with a selective COX-2 inhibitor. Birds in LPS group and saline group were intraperitoneally injected with the same amount of LPS or saline from 14d of age for 3 consecutive days. And birds in the LPS and celecoxib group were given a single intraperitoneal injection of celecoxib 15 min prior to LPS injection at 14 d of age.

Results

The feed intake and body weight gain of broilers were suppressed in response to immune stress induced by LPS which is an intrinsic component of the outer membrane of Gram-negative bacteria. Cyclooxygenase-2 (COX-2), a key enzyme that mediates prostaglandin synthesis, was up-regulated through MAPK-NF-κB pathways in activated microglia cells in broilers exposed to LPS. Subsequently, the binding of prostaglandin E2 (PGE2) to the EP4 receptor maintained the activation of microglia and promoted the secretion of cytokines interleukin-1β and interleukin-8, and chemokines CX3CL1 and CCL4. In addition, the expression of appetite suppressor proopiomelanocortin protein was increased and the levels of growth hormone-releasing hormone were reduced in the hypothalamus. These effects resulted in decreased expression of insulin-like growth factor in the serum of stressed broilers. In contrast, inhibition of COX-2 normalized pro-inflammatory cytokine levels and promoted the expression of Neuropeptide Y and growth hormone-releasing hormone in the hypothalamus which improved the growth performance of stressed broilers. Transcriptomic analysis of the hypothalamus of stressed broilers showed that inhibition of COX-2 activity significantly down-regulated the expression of the TLR1B, IRF7, LY96, MAP3K8, CX3CL1, and CCL4 genes in the MAPK-NF-κB signaling pathway.

Conclusion

This study provides new evidence that immune stress mediates growth suppression in broilers by activating the COX-2-PGE2-EP4 signaling axis. Moreover, growth inhibition is reversed by inhibiting the activity of COX-2 under stressed conditions. These observations suggest new approaches for promoting the health of broiler chickens reared in intensive conditions.

Cloning and expression of kiss genes and regulation of feeding in Siberian sturgeon (Acipenser baerii)

In 1996, kiss was reported to regulate feeding in mammals, but studies are limited in fish. Our study aimed to explore the possible role of kiss in the regulation of feeding in Siberian sturgeon (Acipenser baerii). kiss1 and kiss2 were cloned, and the expression patterns were analyzed in Siberian sturgeon. The complete coding regions of kiss1 and kiss2 genes were 393 and 471 bp. Both kiss1 and kiss2 showed the highest expression level in the hypothalamus. During the periprandial and fasting experiments, the expression of kiss1 and kiss2 highly significantly increased in the hypothalamus after feeding (P < 0.01). Compared with the feeding group, in hypothalamus, kiss1 expression in the fasting group highly significantly decreased (P < 0.01). In contrast, kiss2 expression had no significant difference on days 1 and 7 (P > 0.05) but highly significantly increased on day 14 (P < 0.01). Subsequently, the feeding function was verified by intraperitoneal (i.p.) injection of Kp1(10) and Kp1(10) into fish. The results showed that i.p. injection of 1 µg/g BW Kp1(10) or 0.01 µg/g BW Kp2(10) could significantly reduce 0-1 h food intake (P < 0.05) and affected the expression levels of apelin, ghrelin, leptin, nmu, etc. in the hypothalamus. These results suggested that kiss1 plays an anorexic role in both short- and long-term feeding regulation, while kiss2 plays a short-term anorexic and long-term orexigenic role. This study described kiss as a novel regulator of appetite in fish and laid the groundwork for further studies focused on physiological function. HIGHLIGHTS: • The kiss1 and kiss2 of Siberian sturgeon were cloned. • The expression levels of kiss1 and kiss2 mRNA were the highest in the hypothalamus. • Postprandial hypothalamic kiss1 and kiss2 expression levels increased in the periprandial experiment. • In the fasting test, the expression of hypothalamic kiss1 decreased after fasting, while the expression of kiss2 increased after fasting on the 14th day. • Siberian sturgeon food intake was reduced, and appetite factors expression levels in the hypothalamus were altered after intraperitoneal injection of Kp1(10) and Kp2(10).

Ethanol consumption activates a subset of arcuate nucleus pro-opiomelanocortin (POMC)-producing neurons: a c-fos immunohistochemistry study

Ethanol activates various opioid peptide-containing circuits within the brain that may underlie its motivational and rewarding effects. One component of this circuitry consists of neurons located in the arcuate nucleus (ArcN) of the hypothalamus which express pro-opiomelanocortin (POMC), an opioid precursor peptide that is cleaved to form bioactive fragments including β-endorphin and α-melanocyte stimulating hormone. In this study, we sought to determine if ethanol intake activates ArcN POMC neurons as measured by expression of the immediate early gene c-fos. Male and female POMC-EGFP mice underwent drinking-in-the-dark (DID) procedures for 3 consecutive days (2 h/day) and were allowed to consume either ethanol (20% v/v), saccharin (0.2% w/v), or water. On the fourth day of DID procedures, animals were allowed to consume their respective solutions for 20 min, and 1 h following the session brains were harvested and processed for c-fos immunohistochemistry and co-localization with EGFP. Our results indicate that ethanol intake activates a subset (~15-20%) of ArcN POMC neurons, whereas saccharin or water intake activates significantly fewer (~5-12%) of these neurons. The percent of activated POMC neurons did not correlate with blood ethanol levels at the time of tissue collection, and activation appeared to be distributed throughout the rostrocaudal axis of the ArcN. No sex differences were observed in the degree of neuronal activation across drinking solutions. These findings indicate a preferential activation of ArcN POMC neurons by ethanol consumption, strengthening the notion that ethanol activates endogenous opioid systems in the brain which may underlie its motivational properties.

Intergenerational effects of preconception opioids on glucose homeostasis and hepatic transcription in adult male rats

Adolescence represents a period of significant neurodevelopment during which adverse experiences can lead to prolonged effects on disease vulnerability, including effects that can impact future offspring. Adolescence is a common period for the initiation of drug use, including the use of opioids. Beyond effects on central reward, opioids also impact glucose metabolism, which can impact the risk of diabetes. Moreover, recent animal models suggest that the effects of adolescent opioids can effect glucose metabolism in future offspring. Indeed, we demonstrated that the adult male offspring of females exposed to morphine for 10 days during adolescence (referred to as MORF1 males) are predisposed to the adverse effects of an obesogenic diet. As adults, MORF1 males fed a high fat moderate sucrose diet (FSD) for just 6 weeks had increased fasting glucose and insulin levels when compared to age-matched offspring of females exposed to saline during adolescence (SALF1 males). Clinically, a similar profile of impaired fasting glucose has been associated with hepatic insulin resistance and an increased risk of non-alcoholic fatty liver disease. Thus, in the current study, we used RNA sequencing to determine whether adult MORF1 males demonstrate significant alterations in the hepatic transcriptome suggestive of alterations in metabolism. Age-matched SALF1 and MORF1 males were fed either FSD or control diet (CD) for 8 weeks. Similar to our previous observations, FSD-maintained MORF1 males gained more weight and displayed both fasting hyperglycemia and hyperinsulinemia when compared to FSD-maintained SALF1 males, with no significant effect on glucagon. No differences in bodyweight or fasting-induce glucose were observed in control diet (CD)-maintained F1 males, although there was a trend for CD MORF1 males to display elevated levels of fasting insulin. Unexpectedly, transcriptional analyses revealed profound differences in the hepatic transcriptome of CD-maintained MORF1 and SALF1 (1686 differentially expressed genes) with no significant differences between FSD-maintained MORF1 and SALF1 males. As changes in the hepatic transcriptome were not revealed under 8 weeks FSD conditions, we extended the feeding paradigm and conducted a glucose tolerance test to determine whether impaired fasting glucose observed in FSD MORF1 males was due to peripheral insulin resistance. Impaired glucose tolerance was observed in both CD and FSD MORF1 males, and to a more limited extent in FSD SALF1 males. These findings implicate intergenerational effects of adolescent morphine exposure on the risk of developing insulin resistance and associated comorbidities, even in the absence of an obesogenic diet.

Effects of the POMC System on Glucose Homeostasis and Potential Therapeutic Targets for Obesity and Diabetes

The hypothalamus is indispensable in energy regulation and glucose homeostasis. Previous studies have shown that pro-opiomelanocortin neurons receive both central neuronal signals, such as α-melanocyte-stimulating hormone, β-endorphin, and adrenocorticotropic hormone, as well as sense peripheral signals such as leptin, insulin, adiponectin, glucagon-like peptide-1, and glucagon-like peptide-2, affecting glucose metabolism through their corresponding receptors and related signaling pathways. Abnormalities in these processes can lead to obesity, type 2 diabetes, and other metabolic diseases. However, the mechanisms by which these signal molecules fulfill their role remain unclear. Consequently, in this review, we explored the mechanisms of these hormones and signals on obesity and diabetes to suggest potential therapeutic targets for obesity-related metabolic diseases. Multi-drug combination therapy for obesity and diabetes is becoming a trend and requires further research to help patients to better control their blood glucose and improve their prognosis.

Agouti-related protein as the glucose signaling sensor in the central melanocortin circuits in regulating fish food intake

Agouti-related protein (AgRP) is a neuropeptide synthesized by AgRP/NPY neurons and transcribed as 132 amino acids in humans and 142 amino acids (AgRP1) in Japanese seabass (Lateolabrax maculatus) fish. AgRP neurons are activated by hormonal signals of energy deficits and inhibited by signals of energy surpluses and have been demonstrated to have the ability to sense the dynamics of blood glucose concentrations as the "glucose sensor" in mammals. It is widely recognized that AgRP is an endogenous antagonist of the melanocortin-3 and -4 receptors (MC3R and MC4R) in the hypothalamus, exhibiting potent orexigenic activity and control of energy homeostasis. Most fish, especially carnivorous fish, cannot make efficient use of carbohydrates. When carbohydrates like corn or wheat bran are added as energy sources, they often cause feeding inhibition and metabolic diseases. When fishmeal is replaced by plant protein, this does not completely eliminate carbs, limiting the utilization of carbohydrates and plant proteins in aquaculture. Our previous study showed that AgRP, and not neuropeptide Y (NPY) is the principal protein molecule that correlates well with feeding behavior in Japanese seabass from anorexia to adaptation. The Ghrelin/Leptin-mTOR-S6K1-NPY/AgRP/POMC feed intake regulatory pathway responds to the plant-oriented protein which contains glucose. However, its regulatory function and mechanism are still not clear. This review offers an integrative overview of how glucose signals converge on a molecular level in AgRP neurons of the arcuate nucleus of the hypothalamus. This is in order to control fish food intake and energy homeostasis.

The Beneficial Effects of Essential Oils in Anti-Obesity Treatment

Obesity is a complex disease caused by an excessive amount of body fat. Obesity is a medical problem and represents an important risk factor for the development of serious diseases such as insulin resistance, type 2 diabetes, cardiovascular disease, and some types of cancer. Not to be overlooked are the psychological issues that, in obese subjects, turn into very serious pathologies, such as depression, phobias, anxiety, and lack of self-esteem. In addition to modifying one’s lifestyle, the reduction of body mass can be promoted by different natural compounds such as essential oils (EOs). EOs are mixtures of aromatic substances produced by many plants, particularly in medicinal and aromatic ones. They are odorous and volatile and contain a mixture of terpenes, alcohols, aldehydes, ketones, and esters. Thanks to the characteristics of the various chemical components present in them, EOs are used in the food, cosmetic, and pharmaceutical fields. Indeed, it has been shown that EOs possess great antibiotic, anti-inflammatory, and antitumor powers. Emerging results also demonstrate the anti-obesity effects of EOs. We have examined the main data obtained in experimental studies and, in this review, we summarize the effect of EOs in obesity and obesity-related metabolic diseases.

Neuro-immune-metabolism: The tripod system of homeostasis

Homeostatic regulation of cellular and molecular processes is essential for the efficient physiological functioning of body organs. It requires an intricate balance of several networks throughout the body, most notable being the nervous, immune and metabolic systems. Several studies have reported the interactions between neuro-immune, immune-metabolic and neuro-metabolic pathways. Current review aims to integrate the information and show that neuro, immune and metabolic systems form the triumvirate of homeostasis. It focuses on the cellular and molecular interactions occurring in the extremities and intestine, which are innervated by the peripheral nervous system and for the intestine in particular the enteric nervous system. While the interdependence of neuro-immune-metabolic pathways provides a fallback mechanism in case of disruption of homeostasis, in chronic pathologies of continued disequilibrium, the collapse of one system spreads to the other interacting networks as well. Current review illustrates this domino-effect using diabetes as the main example. Together, this review attempts to provide a holistic picture of the integrated network of neuro-immune-metabolism and attempts to broaden the outlook when devising a scientific study or a treatment strategy.

When Leptin Is Not There: A Review of What Nonsyndromic Monogenic Obesity Cases Tell Us and the Benefits of Exogenous Leptin

Obesity is a pandemic condition of complex etiology, resulting from the increasing exposition to obesogenic environmental factors combined with genetic susceptibility. In the past two decades, advances in genetic research identified variants of the leptin-melanocortin pathway coding for genes, which are related to the potentiation of satiety and hunger, immune system, and fertility. Here, we review cases of congenital leptin deficiency and the possible beneficial effects of leptin replacement therapy. In summary, the cases presented here show clinical phenotypes of disrupted bodily energy homeostasis, biochemical and hormonal disorders, and abnormal immune response. Some phenotypes can be partially reversed by exogenous administration of leptin. With this review, we aim to contribute to the understanding of leptin gene mutations as targets for obesity diagnostics and treatment strategies.

Alcohol consumption preferentially activates a subset of pro-opiomelanocortin (POMC) producing neurons targeting the amygdala

BACKGROUND

Alcohol abuse is a worldwide public health concern and leads to an estimated 90,000 alcohol-related deaths in the United States annually. Alcohol may promote its euphoric and motivational effects, in part, by activating the endogenous opioid system. Pro-opiomelanocortin (POMC) producing neurons located within the arcuate nucleus (ArcN) of the hypothalamus make up one circuit of the endogenous opioid system, and heavily projects to reward-related brain areas such as the amygdala, nucleus accumbens (NAc) and ventral tegmental area (VTA). POMC producing neurons release β-endorphin and other peptides that target opioid receptors within reward areas to elicit their associated rewarding effects. Here we explore ArcN POMC neuronal activation, as assessed via FosB expression, following alcohol consumption to determine whether activation varied within subsets of ArcN POMC projection neurons targeting different reward-related areas.

METHODS

Fluorescent retrobeads were used to label ArcN POMC projection neurons targeting the NAc, amygdala and VTA in POMC-cre mice expressing the reporter tdTomato. Animals (n = 57) were then allowed to voluntarily consume alcohol or water using the drinking-in-the-dark (DID) paradigm, and sacrificed for immunohistochemistry to examine FosB expression within ArcN POMC neurons.

RESULTS

Female mice displayed escalation of alcohol intake across DID sessions, whereas males did not. A greater percent of ArcN POMC neurons target the amygdala over the NAc and VTA, and alcohol consumption preferentially activated ArcN POMC neurons targeting the amygdala over other areas.

CONCLUSION

These findings highlight a novel aspect alcohol-induced activation of the endogenous opioid system, whereby alcohol activates a specific subpopulation of ArcN POMC producing neurons that project primarily to the amygdala.

Effect of combination of peripheral oxytocin and naltrexone at subthreshold doses on food intake, body weight and feeding-related brain gene expression in male rats

In a recent case report involving a male with hypothalamic obesity, concurrent administration of oxytocin (OT) and an opioid receptor antagonist, naltrexone (NTX), synergistically affected energy balance. Here, by using laboratory rats, we examined whether the reported synergy between OT and NTX in the context of food intake extends beyond that one unique case. We found that intravenous OT+NTX combination, at doses subthreshold for each of the drugs individually, decreased episodic consumption of a 10% sucrose solution in non-deprived animals. Daily administration of OT and NTX just before a scheduled, 2-hour, high-fat high-sugar (HFHS) meal over 24 days, decreased cumulative HFHS diet intake, but without a change in body weight due to compensatory standard chow intake during the remainder of the day. The NTX-OT treatment affected expression of several feeding-related genes in the hypothalamus, brain stem and nucleus accumbens, brain regions essential for the regulation of energy- and reward-driven consumption. We conclude that OT and NTX act synergistically to decrease food consumption in rats and that this transient effect is accompanied by changes in brain processes relevant to feeding.

EphrinB1 modulates glutamatergic inputs into POMC-expressing progenitors and controls glucose homeostasis

Proopiomelanocortin (POMC) neurons are major regulators of energy balance and glucose homeostasis. In addition to being regulated by hormones and nutrients, POMC neurons are controlled by glutamatergic input originating from multiple brain regions. However, the factors involved in the formation of glutamatergic inputs and how they contribute to bodily functions remain largely unknown. Here, we show that during the development of glutamatergic inputs, POMC neurons exhibit enriched expression of the Efnb1 (EphrinB1) and Efnb2 (EphrinB2) genes, which are known to control excitatory synapse formation. In vivo loss of Efnb1 in POMC-expressing progenitors decreases the amount of glutamatergic inputs, associated with a reduced number of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor subunits and excitability of these cells. We found that mice lacking Efnb1 in POMC-expressing progenitors display impaired glucose tolerance due to blunted vagus nerve activity and decreased insulin secretion. However, despite reduced excitatory inputs, mice lacking Efnb2 in POMC-expressing progenitors showed no deregulation of insulin secretion and only mild alterations in feeding behavior and gluconeogenesis. Collectively, our data demonstrate the role of ephrins in controlling excitatory input amount into POMC-expressing progenitors and show an isotype-specific role of ephrins on the regulation of glucose homeostasis and feeding.

[Bile acids regulate anorexigenic neuropeptide through p-STAT3-SOCS3 signaling in mouse hypothalamic cells]

OBJECTIVE

To explore the effects of taurolithocholic acid (tLCA) and chenodeoxycholic acid (CDCA) on the expression of aorexigenic neuropeptide in mouse hypothalamus GT1-7 cells.

METHODS

Mouse hypothalamic GT1-7 cells were treated with culture medium containing 10% FBS (control group, n=3) or with 10 nmol/L, 100 nmol/L, 1 μmol/L and 10 μmol/L tLCA (tLCA group, n=3) or CDCA (CDCA group, n=3) for 12, 24 or 48 h. Real-time PCR was performed to determine the expression levels of proopiomelanocortin (POMC) mRNA in the cells, and the production levels of α-melanocyte-stimulating hormone (α-MSH) were assessed using an ELISA kit. Signal transduction and activator of transcription 3 phosphorylation (p-STAT3), threonine kinase phosphorylation (p-AKT), suppressor of cytokine signaling 3 (SOCS3), G protein-coupled bile acid receptor-1 (TGR5) and farnesoid X receptor (FXR) protein were detected by Western blotting.

RESULTS

Western blotting results showed that mouse hypothalamic GT1-7 cells expressed two bile acid receptors, TGR5 and FXR, whose expressions were regulated by bile acids. Real-time PCR showed that the expression of POMC mRNA was significantly increased in the cells after treatment with 10 μmol/L tLCA or CDCA for 24 h. POMC-derived anorexigenic peptide α-MSH increased significantly in GT1-7 cells after treatment with 10 μmol/L tLCA or CDCA for 24 h. Treatment of the cells with tLCA or CDCA significantly increased the expressions of intracellular signaling proteins including p-STAT3, p-AKT and SOCS3.

CONCLUSIONS

Mouse hypothalamic GT1-7 cells express bile acid receptors TGR5 and FXR. Bile acids tLCA or CDCA can promote the expression of POMC mRNA and increase the production of the anorexigenic peptide α-MSH. The intracellular signaling proteins p-AKT, p-STAT3 and SOCS3 are likely involved in bile acid-induced anorexigenic peptide production.

Glucagon-Like Peptide-1 (GLP-1) and 5-Hydroxytryptamine 2c (5-HT2c) Receptor Agonists in the Ventral Tegmental Area (VTA) Inhibit Ghrelin-Stimulated Appetitive Reward

Current literature indicates that the orexigenic peptide ghrelin increases appetitive motivation via signaling in the mesolimbic reward system. Another gastric peptide, glucagon-like peptide-1 (GLP-1), and the neurotransmitter 5-hydroxytryptamine (5-HT), are both known to suppress operant responding for food by acting on key mesolimbic nuclei, including the ventral tegmental area (VTA). In order to investigate the interaction effects of ghrelin, GLP-1, and 5-HT within the VTA, we measured operant responding for sucrose pellets after the administration of ghrelin, the GLP-1 receptor agonist exendin-4 (Ex-4), and the 5-HT_2c receptor agonist Ro60-0175 in male Sprague-Dawley rats. Following training on a progressive ratio 3 (PR3) schedule, animals were first injected with ghrelin into the VTA at doses of 3 to 300 pmol. In subsequent testing, separate rats were administered intraperitoneal (IP) Ex-4 (0.1–1.0 µg/kg) or VTA Ex-4 (0.01–0.1 µg) paired with 300 pmol ghrelin. In a final group of rats, the 5-HT_2c agonist Ro60-0175 was injected IP (0.25–1.0 mg/kg) or into the VTA (1.5–3.0 µg), and under both conditions paired with 300 pmol ghrelin delivered into the VTA. Our results indicated that ghrelin administration increased operant responding for food reward and that this effect was attenuated by IP and VTA Ex-4 pretreatment as well as pre-administration of IP or VTA Ro60-0175. These data provide compelling evidence that mesolimbic GLP-1 and serotonergic circuitry interact with the ghrelinergic system to suppress ghrelin’s effects on the mediation of food reinforcement.

Tumour necrosis factor α induces neuroinflammation and insulin resistance in immortalised hypothalamic neurones through independent pathways

The links between obesity, inflammation and insulin resistance, which are all key characteristics of type 2 diabetes mellitus, are yet to be delineated in the brain. One of the key neuroinflammatory proteins detected in the hypothalamus with over-nutrition is tumour necrosis factor (TNF)α. Using immortalised embryonic rat and mouse hypothalamic cell lines (rHypoE-7 and mHypoE-46) that express orexigenic neuropeptide Y and agouti-related peptide, we investigated changes in insulin signalling and inflammatory gene marker mRNA expression after TNFα exposure. A quantitative polymerase chain reaction array of 84 inflammatory markers (cytokines, chemokines and receptors) demonstrated an increase in the expression of multiple genes encoding inflammatory markers upon exposure to 100 ng mL^-1 TNFα for 4 hours. Furthermore, neurones pre-exposed to TNFα (50 ng mL^-1 ) for 6 or 16 hours exhibited a significant reduction in phosphorylated Akt compared to control after insulin treatment, indicating the attenuation of insulin signalling. mRNA expression of insulin signalling-related genes was also decreased with exposure to TNFα. TNFα significantly increased mRNA expression of IκBα, Tnfrsf1a and IL6 at 4 and 24 hours, activating a pro-inflammatory state. An inhibitor study using an inhibitor of nuclear factor kappa B kinase subunit β (IKK-β) inhibitor, PS1145, demonstrated that TNFα-induced neuroinflammatory marker expression occurs through the IKK-β/nuclear factor-kappa B pathway, whereas oleate, a monounsaturated fatty acid, had no effect on inflammatory markers. To test the efficacy of anti-inflammatory treatment to reverse insulin resistance, neurones were treated with TNFα and PS1145, which did not significantly restore the TNFα-induced changes in cellular insulin sensitivity, indicating that an alternative pathway may be involved. In conclusion, exposure to the inflammatory cytokine TNFα causes cellular insulin resistance and inflammation marker expression in the rHypoE-7 and mHypoE-46 neurones, consistent with effects seen with TNFα in peripheral tissues. It also mimics insulin- and palmitate-induced insulin resistance in hypothalamic neurones. The present study provides further evidence that altered central energy metabolism may be caused by obesity-induced cytokine expression.