Leptin resistance and enhancement of feeding facilitation by melanin-concentrating hormone in mice lacking bombesin receptor subtype-3

Discovery of oridonin as a novel agonist for BRS-3

BACKGROUND

Bombesin Receptor Subtype-3 (BRS-3, Bombesin-like receptor, BB₃) is an orphan G-protein coupled receptor (GPCR). Recent studies have shown that BRS-3 played a vital role in glucose regulation, insulin secretion, and energy homeostasis. Therefore, discovering more novel exogenous ligands with diverse structures for BRS-3 will be of great importance for target validation and drug development.

PURPOSE

In this study, we aim to discover new agonists of BRS-3 from our natural compound libraries, providing a new probe to study the function of BRS-3.

STUDY DESIGN

Multiple cell-based assays and in vivo experiments were performed to identify the new ligand.

METHODS

BRS-3 overexpression cells were coupled with FLIPR assay, homogeneous time-resolved fluorescence (HTRF) IP-ONE assay, dynamic mass redistribution (DMR) assay, β-arrestin2 recruitment assay, and western blot to determine receptor activation and downstream signaling events. To further validate the target of BRS-3, a series of in vitro and in vivo experiences were conducted, including glucose uptake, glucose transporter type 4 (GLUT4) transportation in C2C12, and oral glucose tolerance test (OGTT) in mice.

RESULTS

We discovered and identified oridonin as a novel small molecule agonist of BRS-3, with a moderate affinity (EC₅₀ of 2.236 × 10^-7 M in calcium mobilization assay), specificity, and subtype selectivity. Further in vitro and in vivo tests demonstrated that oridonin exerted beneficial effects in glucose homeostasis through activating BRS-3.

CONCLUSIONS

Oridonin, as the discovered new ligand of BRS-3, provides a valuable tool compound to investigate BRS-3's function, especially for target validation in type 2 diabetes and obesity. Oridonin is promising as a lead compound in the treatment of metabolic disorders. Compared to the known agonists of BRS-3, we can take advantage of the multiple reported pharmacological activities of ODN as a natural product and assess whether these pharmacological activities are regulated by BRS-3. This may facilitate the discovery of novel functions of BRS-3.

High-Throughput Screening of Mouse Gene Knockouts Identifies Established and Novel High Body Fat Phenotypes

PURPOSE

Obesity is a major public health problem. Understanding which genes contribute to obesity may better predict individual risk and allow development of new therapies. Because obesity of a mouse gene knockout (KO) line predicts an association of the orthologous human gene with obesity, we reviewed data from the Lexicon Genome5000TM high throughput phenotypic screen (HTS) of mouse gene KOs to identify KO lines with high body fat.

MATERIALS AND METHODS

KO lines were generated using homologous recombination or gene trapping technologies. HTS body composition analyses were performed on adult wild-type and homozygous KO littermate mice from 3758 druggable mouse genes having a human ortholog. Body composition was measured by either DXA or QMR on chow-fed cohorts from all 3758 KO lines and was measured by QMR on independent high fat diet-fed cohorts from 2488 of these KO lines. Where possible, comparisons were made to HTS data from the International Mouse Phenotyping Consortium (IMPC).

RESULTS

Body fat data are presented for 75 KO lines. Of 46 KO lines where independent external published and/or IMPC KO lines are reported as obese, 43 had increased body fat. For the remaining 29 novel high body fat KO lines, Ksr2 and G2e3 are supported by data from additional independent KO cohorts, 6 (Asnsd1, Srpk2, Dpp8, Cxxc4, Tenm3 and Kiss1) are supported by data from additional internal cohorts, and the remaining 21 including Tle4, Ak5, Ntm, Tusc3, Ankk1, Mfap3l, Prok2 and Prokr2 were studied with HTS cohorts only.

CONCLUSION

These data support the finding of high body fat in 43 independent external published and/or IMPC KO lines. A novel obese phenotype was identified in 29 additional KO lines, with 27 still lacking the external confirmation now provided for Ksr2 and G2e3 KO mice. Undoubtedly, many mammalian obesity genes remain to be identified and characterized.

Bombesin receptor subtype-3-expressing neurons regulate energy homeostasis through a novel neuronal pathway in the hypothalamus

OBJECTIVES

Bombesin receptor subtype-3 (BRS-3) has been suggested to play a potential role in energy homeostasis. However, the physiological mechanism of BRS-3 on energy homeostasis remains unknown. Thus, we investigated the BRS-3-mediated neuronal pathway involved in food intake and energy expenditure.

MATERIALS AND METHODS

Expression of BRS-3 in the rat brain was histologically examined. The BRS-3 neurons activated by refeeding-induced satiety or a BRS-3 agonist were identified by c-Fos immunostaining. We also analyzed expression changes in feeding-relating peptides in the brain of fasted rats administered with the BRS-3 agonist.

RESULTS

In the paraventricular hypothalamic nucleus (PVH), dorsomedial hypothalamic nucleus (DMH), and medial preoptic area (MPA), strong c-Fos induction was observed in the BRS-3 neurons especially in PVH after refeeding. However, the BRS-3 neurons in the PVH did not express feeding-regulating peptides, while the BRS-3 agonist administration induced c-Fos expression in the DMH and MPA, which were not refeeding-sensitive, as well as in the PVH. The BRS-3 agonist administration changed the Pomc and Cart mRNA level in several brain regions of fasted rats.

CONCLUSION

These results suggest that BRS-3 neurons in the PVH are a novel functional subdivision in the PVH that regulates feeding behavior. As the MPA and DMH are reportedly involved in thermoregulation and energy metabolism, the BRS-3 neurons in the MPA/DMH might mediate the energy expenditure control. POMC and CART may contribute to BRS-3 neuron-mediated energy homeostasis regulation. In summary, BRS-3-expressing neurons could regulate energy homeostasis through a novel neuronal pathway.

Insights into bombesin receptors and ligands: Highlighting recent advances

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

Bombesin receptor subtype 3 as a potential target for obesity and diabetes

INTRODUCTION

Diabetes mellitus and obesity are important health issues; increasing in prevalence, both in the USA and globally. There are only limited pharmacological treatments, and although bariatric surgery is effective, new effective pharmacologic treatments would be of great value. This review covers one area of increasing interest that could yield new novel treatments of obesity/diabetes mellitus. It involves recognition of the central role the G-protein-coupled receptor, bombesin receptor subtype 3 (BRS-3) plays in energy/glucose metabolism.

AREAS COVERED

Since the initial observation that BRS-3 knockout mice develop obesity, hypertension, impaired glucose metabolism and hyperphagia, there have been numerous studies of the mechanisms involved and the development of selective BRS-3 agonists/antagonists, which have marked effects on body weight, feeding and glucose/insulin homeostasis. In this review, each of these areas is briefly reviewed.

EXPERT OPINION

BRS-3 plays an important role in glucose/energy homeostasis. The development of potent, selective BRS-3 agonists demonstrates promise as a novel approach to treat obesity/diabetic states. One important question that needs to be addressed is whether BRS-3 agonists need to be centrally acting. This is particularly important in light of recent animal and human studies that report transient cardiovascular side effects with centrally acting oral BRS agonists.

Comparative pharmacology of bombesin receptor subtype-3, nonpeptide agonist MK-5046, a universal peptide agonist, and peptide antagonist Bantag-1 for human bombesin receptors

Bombesin-receptor-subtype-3 (BRS-3) is an orphan G-protein-coupled receptor of the bombesin (Bn) family whose natural ligand is unknown and which does not bind any natural Bn-peptide with high affinity. It is present in the central nervous system, peripheral tissues, and tumors; however, its role in normal physiology/pathophysiology is largely unknown because of the lack of selective ligands. Recently, MK-5046 [(2S)-1,1,1-trifluoro-2-[4-(1H-pyrazol-1-yl)phenyl]-3-(4-{[1-(trifluoromethyl)cyclopropyl]methyl}-1H-imidazol-2-yl)propan-2-ol] and Bantag-1 [Boc-Phe-His-4-amino-5-cyclohexyl-2,4,5-trideoxypentonyl-Leu-(3-dimethylamino) benzylamide N-methylammonium trifluoroacetate], a nonpeptide agonist and a peptide antagonist, respectively, for BRS-3 have been described, but there have been limited studies on their pharmacology. We studied MK-5046 and Bantag-1 interactions with human Bn-receptors-human bombesin receptor subtype-3 (hBRS-3), gastrin-releasing peptide receptor (GRP-R), and neuromedin B receptor (NMB-R)-and compared them with the nonselective, peptide-agonist [d-Tyr6,βAla11,Phe13,Nle14]Bn-(6-14) (peptide #1). Receptor activation was detected by activation of phospholipase C (PLC), mitogen-activated protein kinase (MAPK), focal adhesion kinase (FAK), paxillin, and Akt. In hBRS-3 cells, the relative affinities were Bantag-1 (1.3 nM) > peptide #1 (2 nM) > MK-5046 (37-160 nM) > GRP, NMB (>10 μM), and the binding-dose-inhibition curves were broad (>4 logs), with Hill coefficients differing significantly from unity. Curve-fitting demonstrated high-affinity (MK-5046, Ki = 0.08 nM) and low-affinity (MK-5046, Ki = 11-29 nM) binding sites. For PLC activation in hBRS-3 cells, the relative potencies were MK-5046 (0.02 nM) > peptide #1 (6 nM) > GRP, NMB, Bantag-1 (>10 μM), and MK-5046 had a biphasic dose response, whereas peptide #1 was monophasic. Bantag-1 was a specific hBRS-3-antagonist. In hBRS-3 cells, MK-5046 was a full agonist for activation of MAPK, FAK, Akt, and paxillin; however, it was a partial agonist for phospholipase A2 (PLA2) activation. The kinetics of activation/duration of action for PLC/MAPK activation of MK-5046 and peptide #1 differed, with peptide #1 causing more rapid stimulation; however, MK-5046 had more prolonged activity. Our study finds that MK-5046 and Bantag-1 have high affinity/selectivity for hBRS-3. The nonpeptide MK-5046 and peptide #1 agonists differ markedly in their receptor coupling, ability to activate different signaling cascades, and kinetics/duration of action. These results show that their hBRS-3 receptor activation is not always concordant and could lead to markedly different cellular responses.

Biology and pharmacology of bombesin receptor subtype-3

PURPOSE OF REVIEW

This review summarizes the results of recent studies regarding the biology and pharmacology of novel synthetic agonists and antagonists of the bombesin receptor subtype-3 (BRS-3).

RECENT FINDINGS

All three mammalian bombesin receptors including gastrin-releasing peptide receptor, the neuromedin B receptor, and the BRS-3 have been shown to regulate energy balance and appetite and satiety. Studies indicate that the orphan BRS-3 is an important regulator of body weight, energy expenditure, and glucose homeostasis. Endogenous bombesin-like peptides bombesin, gastrin-releasing peptide, and neuromedin B receptor do not bind to BRS-3 and the endogenous BRS-3 ligand remains unknown. The novel synthesis of selective, high-affinity BRS-3 agonists and antagonists has recently been accomplished and showed that BRS-3 regulates energy balance independent of other established pathways and glucose-stimulated insulin secretion in the pancreatic islet cells. The availability of new BRS-3 selective agonists and antagonists will facilitate further elucidation of its role in energy homeostasis, and provides a potential approach for the pharmacological treatment of obesity and type 2 diabetes.

SUMMARY

The native ligand of the G protein-coupled BRS-3 has not been identified as of now. However, novel synthesis of small-molecule, high-affinity agonists and antagonists on the BRS-3 was used in the recent studies and demonstrated an important role of BRS-3 in the regulation of energy homeostasis and glucose metabolism.

Appetite-modifying effects of bombesin receptor subtype-3 agonists

Studies on bombesin-like peptides (BLP) and their respective mammalian receptors (Bn-r) have demonstrated a significant biological impact on a broad array of physiological and pathophysiological conditions. Pharmacological experiments in vitro and in vivo as well as utilization of genetic rodent models of the gastrin-releasing peptide receptor (GRP-R/BB2-receptor), neuromedin B receptor (NMB-R/BB1-receptor), and the bombesin receptor subtype-3 (BRS-3/BB3-receptor) further delineated their role in health and disease. All three mammalian bombesin receptors have been shown to possess some role in the regulation of energy balance and appetite and satiety. Compelling experimental evidence has accumulated indicating that the orphan BRS-3 is an important regulator of body weight, energy expenditure, and glucose homeostasis. BRS-3 possesses no high affinity to the endogenous bombesin-like peptides (BLP) bombesin, GRP, and NMB, and its endogenous ligand remains unknown. Recently, the synthesis of novel, selective high-affinity BRS-3 agonists and antagonists has been accomplished and has demonstrated that BRS-3 regulates energy balance independent of other established pathways. Accordingly, the availability of new BRS-3 selective agonists and antagonists will facilitate further elucidation of its role in energy homeostasis and provides a potential approach for the pharmacological treatment of obesity.

Bombesin receptor subtype-3 (BRS-3) regulates glucose-stimulated insulin secretion in pancreatic islets across multiple species

Bombesin receptor subtype-3 (BRS-3) regulates energy homeostasis, and BRS-3 agonism is being explored as a possible therapy for obesity. Here we study the role of BRS-3 in the regulation of glucose-stimulated insulin secretion (GSIS) and glucose homeostasis. We quantified BRS-3 mRNA in pancreatic islets from multiple species and examined the acute effects of Bag-1, a selective BRS-3 agonist, on GSIS in mouse, rat, and human islets, and on oral glucose tolerance in mice. BRS-3 is highly expressed in human, mouse, rhesus, and dog (but not rat) pancreatic islets and in rodent insulinoma cell lines (INS-1 832/3 and MIN6). Silencing BRS-3 with small interfering RNA or pharmacological blockade with a BRS-3 antagonist, Bantag-1, reduced GSIS in 832/3 cells. In contrast, the BRS-3 agonist (Bag-1) increased GSIS in 832/3 and MIN6 cells. The augmentation of GSIS by Bag-1 was completely blocked by U73122, a phospholipase C inhibitor. Bag-1 also enhanced GSIS in islets isolated from wild-type, but not Brs3 knockout mice. In vivo, Bag-1 reduced glucose levels during oral glucose tolerance test in a BRS-3-dependent manner. BRS-3 agonists also increased GSIS in human islets. These results identify a potential role for BRS-3 in islet physiology, with agonism directly promoting GSIS. Thus, in addition to its potential role in the treatment of obesity, BRS-3 may also regulate blood glucose levels and have a role in the treatment of diabetes mellitus.

Treating obesity? It's in the bag!

BRS-3 is an orphan G protein coupled receptor highly expressed in the brain. Pharmacological studies in this issue (Guan et al., 2010) further support a role for this receptor in energy homeostasis and show that the BRS-3 agonist Bag-1 effectively causes weight loss by decreasing food intake and increasing metabolic rate.

Regulation and signaling of human bombesin receptors and their biological effects

PURPOSE OF REVIEW

This review will highlight recent advances in the understanding of molecular mechanisms by which mammalian bombesin receptors are regulated and which intracellular signaling pathways have been characterized to mediate agonist-dependent receptor biological effects.

RECENT FINDINGS

Mammalian bombesin receptors have been demonstrated to be involved in a larger array of physiological and pathophysiological conditions than previously reported. Pharmacological experiments in vitro and in vivo as well as utilization of animals genetically deficient of the gastrin-releasing peptide receptor demonstrated roles in memory and fear behavior, lung development and injury, small intestinal cell repair, autocrine tumor growth, and mediating signals for pruritus and penile reflexes. Intracellular signaling studies predominantly of the gastrin-releasing peptide receptor owing to its frequent overexpression in some human malignancies showed that PI3 kinase activation is an important mechanism of cell proliferation. Tumor cell treatment including gastrin-releasing peptide receptor antagonists combined with inhibition of epidermal growth factor receptor resulted in an additive effect on blocking cell proliferation. Novel molecular mechanisms of the orphan bombesin receptor subtype-3 and gastrin-releasing peptide receptor gene regulation have been elucidated.

SUMMARY

Inhibition of gastrin-releasing peptide receptor signaling in human malignancies represents an attractive target for pharmacological treatment. Novel functions of bombesin related peptides have been identified including processes in the central nervous system, lung and intestinal tract.

High-throughput screening of mouse knockout lines identifies true lean and obese phenotypes

We developed a high-throughput approach to knockout (KO) and phenotype mouse orthologs of the 5,000 potential drug targets in the human genome. As part of the phenotypic screen, dual-energy X-ray absorptiometry (DXA) technology estimates body-fat stores in eight KO and four wild-type (WT) littermate chow-fed mice from each line. Normalized % body fat (nBF) (mean KO % body fat/mean WT littermate % body fat) values from the first 2322 lines with viable KO mice at 14 weeks of age showed a normal distribution. We chose to determine how well this screen identifies body-fat phenotypes by selecting 13 of these 2322 KO lines to serve as benchmarks based on their published lean or obese phenotype on a chow diet. The nBF values for the eight benchmark KO lines with a lean phenotype were > or =1 s.d. below the mean for seven (perilipin, SCD1, CB1, MCH1R, PTP1B, GPAT1, PIP5K2B) but close to the mean for NPY Y4R. The nBF values for the five benchmark KO lines with an obese phenotype were >2 s.d. above the mean for four (MC4R, MC3R, BRS3, translin) but close to the mean for 5HT2cR. This screen also identifies novel body-fat phenotypes as exemplified by the obese kinase suppressor of ras 2 (KSR2) KO mice. These body-fat phenotypes were confirmed upon studying additional cohorts of mice for KSR2 and all 13 benchmark KO lines. This simple and cost-effective screen appears capable of identifying genes with a role in regulating mammalian body fat.

International Union of Pharmacology. LXVIII. Mammalian bombesin receptors: nomenclature, distribution, pharmacology, signaling, and functions in normal and disease states

The mammalian bombesin receptor family comprises three G protein-coupled heptahelical receptors: the neuromedin B (NMB) receptor (BB(1)), the gastrin-releasing peptide (GRP) receptor (BB(2)), and the orphan receptor bombesin receptor subtype 3 (BRS-3) (BB(3)). Each receptor is widely distributed, especially in the gastrointestinal (GI) tract and central nervous system (CNS), and the receptors have a large range of effects in both normal physiology and pathophysiological conditions. The mammalian bombesin peptides, GRP and NMB, demonstrate a broad spectrum of pharmacological/biological responses. GRP stimulates smooth muscle contraction and GI motility, release of numerous GI hormones/neurotransmitters, and secretion and/or hormone release from the pancreas, stomach, colon, and numerous endocrine organs and has potent effects on immune cells, potent growth effects on both normal tissues and tumors, potent CNS effects, including regulation of circadian rhythm, thermoregulation; anxiety/fear responses, food intake, and numerous CNS effects on the GI tract as well as the spinal transmission of chronic pruritus. NMB causes contraction of smooth muscle, has growth effects in various tissues, has CNS effects, including effects on feeding and thermoregulation, regulates thyroid-stimulating hormone release, stimulates various CNS neurons, has behavioral effects, and has effects on spinal sensory transmission. GRP, and to a lesser extent NMB, affects growth and/or differentiation of various human tumors, including colon, prostate, lung, and some gynecologic cancers. Knockout studies show that BB(3) has important effects in energy balance, glucose homeostasis, control of body weight, lung development and response to injury, tumor growth, and perhaps GI motility. This review summarizes advances in our understanding of the biology/pharmacology of these receptors, including their classification, structure, pharmacology, physiology, and role in pathophysiological conditions.

Factors contributing to obesity in bombesin receptor subtype-3-deficient mice

Mice with a targeted disruption of bombesin receptor subtype-3 (BRS-3 KO) develop hyperphagia, obesity, hypertension, and impaired glucose metabolism. However, the factors contributing to their phenotype have not been clearly established. To determine whether their obesity is a result of increased food intake or a defect in energy regulation, we matched the caloric intake of BRS-3 KO mice to wild-type (WT) ad libitum (ad lib)-fed controls over 21 wk. Although BRS-3 KO ad lib-fed mice were 29% heavier, the body weights of BRS-3 KO pair-fed mice did not differ from WT ad lib-fed mice. Pair-feeding BRS-3 KO mice normalized plasma insulin but failed to completely reverse increased adiposity and leptin levels. Hyperphagia in ad lib-fed KO mice was due to an increase in meal size without a compensatory decrease in meal frequency resulting in an increase in total daily food intake. An examination of neuropeptide Y, proopiomelanocortin, and agouti-related peptide gene expression in the arcuate nucleus revealed that BRS-3 KO mice have some deficits in their response to energy regulatory signals. An evaluation of the satiety effects of cholecystokinin, bombesin, and gastrin-releasing peptide found no differences in feeding suppression by these peptides. We conclude that hyperphagia is a major factor leading to increased body weight and hyperinsulinemia in BRS-3 KO mice. However, our finding that pair-feeding did not completely normalize fat distribution and plasma leptin levels suggests there is also a metabolic dysregulation that may contribute to, or sustain, their obese phenotype.

Role of neuropeptides in appetite regulation and obesity--a review

Obesity represents the most prevalent nutritional problem worldwide which in the long run predisposes to development of diabetes mellitus, hypertension, endometrial carcinoma, osteoarthritis, gall stones and cardiovascular diseases. Despite significant reductions in dietary fat consumption, the prevalence of obesity is on a rise and is taking on pandemic proportions. Obesity develops when energy intake exceeds energy expenditure over time. Recently, a close evolutionary relationship between the peripheral and hypothalamic neuropeptides has become apparent. The hypothalamus being the central feeding organ mediates regulation of short-term and long-term dietary intake via synthesis of various orexigenic and anorectic neuropeptides. The structure and function of many hypothalamic peptides (neuropeptide Y (NPY), melanocortins, agouti-related peptide (AGRP), cocaine and amphetamine regulated transcript (CART), melanin concentrating hormone (MCH), orexins have been characterized in rodent models The peripheral neuropeptides such as cholecystokinin (CCK), ghrelin, peptide YY (PYY3-36), amylin, bombesin regulate important gastrointestinal functions such as motility, secretion, absorption, provide feedback to the central nervous system on availability of nutrients and may play a part in regulating food intake. The pharmacological potential of several endogenous peripheral peptides released prior to, during and/or after feeding are being explored. Long-term regulation is provided by the main circulating hormones leptin and insulin. These systems implicated in hypothalamic appetite regulation provide potential targets for treatment of obesity which could potentially pass into clinical development in the next 5 years. This review summarizes various effects and interrelationship of these central and peripheral neuropeptides in metabolism, obesity and their potential role as targets for treatment of obesity.

Young adult-specific hyperphagia in diabetic Goto-kakizaki rats is associated with leptin resistance and elevation of neuropeptide Y mRNA in the arcuate nucleus

The present study aimed to examine whether hyperphagia, which is frequently observed in type 1 diabetic patients and model animals, also occurs in type 2 diabetic Goto-Kakizaki (GK) rats and, if so, to explore underlying abnormalities in the hypothalamus. GK rats at postnatal weeks 6-12, compared to control Wistar rats, exhibited hyperphagia, hyperglycaemia, hyperleptinemia and increased visceral fat accumulation, whereas body weight was unaltered. The ability of leptin to suppress feeding was reduced in GK rats compared to Wistar rats of these ages. In GK rats, leptin-induced phosphorylation of signal transducer and activator of transcription 3 was significantly reduced in the cells of the hypothalamic arcuate nucleus (ARC), but not of the ventromedial hypothalamus, whereas the mRNA level of functional leptin receptor was unaltered. By real-time polymerase chain reaction and in situ hybridisation, mRNA levels of neuropeptide Y, but not pro-opiomelanocortin and galanin-like peptide, were significantly increased in the ARC of GK rats at 11 weeks, but not 26 weeks. Following i.c.v. injection of a NPY Y1 antagonist, 1229U91, the amount of food intake in GK rats was indistinguishable from that in Wistar rats, thus eliminating the hyperphagia of GK rats. These results demonstrate that young adult GK rats display hyperphagia in association with leptin resistance and increased NPY mRNA level in the ARC.

Expanding the scales: The multiple roles of MCH in regulating energy balance and other biological functions

Melanin-concentrating hormone (MCH) is a cyclic peptide originally identified as a 17-amino-acid circulating hormone in teleost fish, where it is secreted by the pituitary in response to stress and environmental stimuli. In fish, MCH lightens skin color by stimulating aggregation of melanosomes, pigment-containing granules in melanophores, cells of neuroectodermal origin found in fish scales. Although the peptide structure between fish and mammals is highly conserved, in mammals, MCH has no demonstrable effects on pigmentation; instead, based on a series of pharmacological and genetic experiments, MCH has emerged as a critical hypothalamic regulator of energy homeostasis, having effects on both feeding behavior and energy expenditure.

Further insights into the neurobiology of melanin-concentrating hormone in energy and mood balances

Melanin-concentrating hormone (MCH) is a critical hypothalamic anabolic neuropeptide, with key central and peripheral actions on energy balance regulation. The actions of MCH are, so far, known to be transduced through two seven-transmembrane-like receptor paralogues, named MCH1R and MCH2R. MCH2R is not functional in rodents. MCH1R is an important receptor involved in mediating feeding behaviour modulation by MCH in rodents. Pharmacological antagonism at MCH1R in rodents diminishes food intake and results in significant and sustained weight loss in fat tissues, particularly in obese animals. Additionally, MCH1R antagonists have been shown to have anxiolytic and antidepressant properties. The purpose of this review is to highlight the recent numerous pieces of evidence showing that pharmacological blockade at MCH1R could be a potential treatment for obesity and its related metabolic syndrome, as well as for various psychiatric disorders.

Expression of feeding-related peptide receptors mRNA in GT1-7 cell line and roles of leptin and orexins in control of GnRH secretion

AIM

To investigate the expression of feeding-related peptide receptors mRNA in GT1-7 cell line and roles of leptin and orexins in the control of GnRH secretion.

METHODS

Receptors of bombesin3, cholecystokinin (CCK)-A, CCK-B, glucagon-like peptide (GLP)1, melanin-concentrating hormone (MCH)1, orexin1, orexin2, neuromedin-B, neuropeptide Y (NPY)1 and NPY5, neurotensin (NT)1, NT2, NT3, and leptin receptor long form mRNA in GT1-7 cells were detected by reversed transcriptase-polymerase chain reaction. GT1-7 cells were treated with leptin, orexin A and orexin B at a cohort of concentrations for different lengths of time, and GnRH in medium was determined by radioimmunoassay (RIA).

RESULTS

Receptors of bombesin 3, CCK-B, GLP1, MCH1, orexin1, neuromedin-B, NPY1, NPY5, NT1, NT3, and leptin receptor long form mRNA were expressed in GT1-7 cells, of which, receptors of GLP1, neuromedin-B, NPY1, and NT3 were highly expressed. No amplified fragments of orexin2, NT2, and CCK-A receptor cDNA were generated with GT1-7 RNA, indicating that the GT1-7 cells did not express mRNA of them. Leptin induced a significant stimulation of GnRH release, the results being most significant at 0.1 nmol/L for 15 min. In contrast to other studies in hypothalamic explants, neither orexin A nor orexin B affected basal GnRH secretion over a wide range of concentrations ranging from 1 nmol/L to 500 nmol/Lat 15, 30, and 60 min.

CONCLUSION

Feeding and reproductive function are closely linked. Many orexigenic and anorexigenic signals may control feeding behavior as well as alter GnRH secretion through their receptors on GnRH neurons.