Neurosecretory Protein GL, a Hypothalamic Small Secretory Protein, Participates in Energy Homeostasis in Male Mice

Recent Research on Mechanisms of Feeding Regulation in Chicks

Food intake affects poultry productivity. A complete understanding of these regulatory mechanisms provides new strategies to improve productivity. Food intake is regulated by complex mechanisms involving many factors, including the central nervous system, gastrointestinal tract, hormones, and nutrients. Although several studies have been conducted to elucidate regulatory mechanisms in chickens, the mechanisms remain unclear. To update the current knowledge on feeding regulation in chickens, this review focuses on recent findings that have not been summarized in previous reviews, including spexins, adipokines, neurosecretory proteins GL and GM, and central intracellular signaling factors.

Expression of mRNAs Encoding Hypothalamic Small Proteins, Neurosecretory Protein GL and Neurosecretory Protein GM, in the Japanese Quail, Coturnix japonica

Neurosecretory protein GL (NPGL) and neurosecretory protein GM (NPGM) are novel neuropeptides that have been discovered in the hypothalamic infundibulum of chickens. NPGL and NPGM play important roles in lipid metabolism in juvenile chickens. The physiological functions of NPGL and NPGM in sexually mature birds remain unknown. The Japanese quail (Coturnix japonica) seems to be an appropriate model for analyzing NPGL and NPGM during sexual maturity. However, studies on NPGL or NPGM have yet to be reported in the Japanese quail. In the present study, we identified cDNAs encoding precursor proteins of NPGL and NPGM in the quail hypothalamus. In situ hybridization revealed that NPGL mRNA-expressing cells in the hypothalamus were localized in the infundibular nucleus and median eminence, and NPGM mRNA-expressing cells were only found in the mammillary nucleus. Immunohistochemistry revealed that NPGM-like immunoreactive cells were distributed in the mammillary nucleus, whereas NPGL-like immunoreactive cells were not detected in the hypothalamus. Real-time PCR analysis indicated that the expression of NPGL mRNA was higher in the hypothalamus of females than in that of males, and NPGM mRNA expression showed no sex differences. NPGL and NPGM mRNA expression in males was upregulated after 24 h of food deprivation. In females, only NPGM mRNA expression was increased by fasting. These results suggest that the physiological functions of NPGL and NPGM are different in quail, and these factors are involved in sex differences in energy metabolism.

Neurosecretory Protein GM-Expressing Neurons Participate in Lipid Storage and Inflammation in Newly Developed Cre Driver Male Mice

Obesity induces inflammation in the hypothalamus and adipose tissue, resulting in metabolic disorders. A novel hypothalamic neuropeptide, neurosecretory protein GM (NPGM), was previously identified in the hypothalamus of vertebrates. While NPGM plays an important role in lipid metabolism in chicks, its metabolic regulatory effects in mammals remain unclear. In this study, a novel Cre driver line, NPGM-Cre, was generated for cell-specific manipulation. Cre-dependent overexpression of Npgm led to fat accumulation without increased food consumption in male NPGM-Cre mice. Chemogenetic activation of NPGM neurons in the hypothalamus acutely promoted feeding behavior and chronically resulted in a transient increase in body mass gain. Furthermore, the ablated NPGM neurons exhibited a tendency to be glucose intolerant, with infiltration of proinflammatory macrophages into the adipose tissue. These results suggest that NPGM neurons may regulate lipid storage and inflammatory responses, thereby maintaining glucose homeostasis.

Nanomolar range of FAM237B can activate receptor GPR83

Our recent study confirmed that the mature neuropeptide FAM237A, also known as neurosecretory protein GL (NPGL), is an efficient agonist for GPR83. The paralog FAM237B was previously reported as a weak agonist for GPR83. In the present study, we prepared mature human FAM237B via an intein-fusion approach and demonstrated that it could cause a significant activation effect at the nanomolar range (1‒10 nM) in a NanoBiT-based β-arrestin recruitment assay. Thus, FAM237B appears to be another endogenous agonist for GPR83 and future in vivo studies will be required to confirm this.

Profiling mouse brown and white adipocytes to identify metabolically relevant small ORFs and functional microproteins

Microproteins (MPs) are a potentially rich source of uncharacterized metabolic regulators. Here, we use ribosome profiling (Ribo-seq) to curate 3,877 unannotated MP-encoding small ORFs (smORFs) in primary brown, white, and beige mouse adipocytes. Of these, we validated 85 MPs by proteomics, including 33 circulating MPs in mouse plasma. Analyses of MP-encoding mRNAs under different physiological conditions (high-fat diet) revealed that numerous MPs are regulated in adipose tissue in vivo and are co-expressed with established metabolic genes. Furthermore, Ribo-seq provided evidence for the translation of Gm8773, which encodes a secreted MP that is homologous to human and chicken FAM237B. Gm8773 is highly expressed in the arcuate nucleus of the hypothalamus, and intracerebroventricular administration of recombinant mFAM237B showed orexigenic activity in obese mice. Together, these data highlight the value of this adipocyte MP database in identifying MPs with roles in fundamental metabolic and physiological processes such as feeding.

Neurosecretory protein GL in GIFT tilapia (Oreochromis niloticus): cDNA cloning, tissue distribution and effects of feeding on its expression

Neurosecretory protein GL (NPGL), a novel neuropeptide, has been identified in the hypothalamus of chicks and rodents. NPGL plays a crucial role in monitoring energetic status via the regulation of feeding and metabolism. However, no study on NPGL has been reported in fish thus far. In the present study, the full-length cDNA of NPGL was identified from the hypothalamus of GIFT tilapia (Oreochromis niloticus). The ORF of tilapia NPGL is 471 bp and encodes a precursor peptide with a size of 156 a.a, consisting of a 26 a.a signal peptide and an 82 a.a mature peptide. Tissue distribution profiles of npgl in tilapia were acquired using semiquantitative PCR and in situ hybridization (ISH). The results showed that the highest npgl mRNA is expressed in the telencephalic-preoptic complex, which comprises both the telencephalon and the anterior preoptic area (POA) of male tilapia, and in the ovary of female tilapia. In addition, in male tilapia, the ISH results showed that the cells containing npgl mRNA were distributed exclusively in the anterior periventricular pretectal nucleus (Ppa) of the POA. FISH results demonstrated that npgl mRNA is also expressed in the lateral tuberal nucleus of the hypothalamus (NLT). Real-time PCR showed that npgl mRNA significantly increased in the telencephalic-preoptic complex of male tilapia that were fasted for 24 h and then fed a full diet for 20 min compared with the unfed group. Results of the FISH study showed that parvocellular cells containing npgl mRNA in the Ppa of fed fish were apparently more abundant than those of the unfed group. Few npgl positive signals also appeared in the NLT after full feeding, where pomc mRNA is highly expressed. These results indicate that NPGL may be a short-term satiety factor in fish and that the coexpression of NPGL and POMC may be present in the hypothalamus of male tilapia.

Neurosecretory Protein GL Promotes Normotopic Fat Accumulation in Male ICR Mice

Neurosecretory protein GL (NPGL) is a small secretory protein identified in the hypothalamus of birds and mammals. We recently reported that NPGL exerts obesogenic effects in obesity-prone C57BL6/J mice. However, whether NPGL elicits adiposity in different mouse strains is poorly understood. In this study, we generated transgenic mice overexpressing Npgl using the ICR strain (Npgl Tg mice) to elucidate the obesogenic effects of NPGL in different strains. Npgl Tg mice showed increased white adipose tissue (WAT) mass. Although the mass of brown adipose tissue (BAT) was slightly altered in Npgl Tg mice, hypertrophy of lipid droplets was also observed in BAT. In contrast, fat accumulation was not induced in the liver, with the upregulation of mRNAs related to hepatic lipolysis. These results support the hypothesis that NPGL causes obesity in several strains and species. This report highlights the pivotal role of NPGL in fat accumulation in adipose tissues and contributes to the elucidation of the biological mechanisms underlying obesity and metabolic diseases in heterogeneous populations.

Effect of Stressors on the mRNA Expressions of Neurosecretory Protein GL and Neurosecretory Protein GM in Chicks

We recently discovered novel cDNAs encoding the precursors of two small secretory proteins, neurosecretory protein GL (NPGL) and neurosecretory protein GM (NPGM), in the mediobasal hypothalamus (MBH) of chickens. In addition, we found colocalization of NPGL, NPGM, and histidine decarboxylase (HDC; histamine-producing enzyme) in same neurons of the medial mammillary nucleus of the hypothalamus. In this study, we elucidated the effect of several stresses, including food deprivation, environmental heat, inflammation, and social isolation, on the mRNA expression of NPGL, NPGM, and HDC in chicks using real-time PCR. Food deprivation for 24 h increased NPGM mRNA expression in the MBH. On the other hand, an environmental temperature of 37°C for 24 h did not affect their mRNA expression. Six hours after intraperitoneal injection of lipopolysaccharide, an inducer of inflammation, the mRNA expression of NPGM, but not that of NPGL and HDC increased. Social isolation for 3 h induced an increase in the mRNA expression of NPGL, NPGM, and HDC. These results indicate that NPGM, but not NPGL or HDC, may participate in several physiological responses to stress in chicks.

Immunohistochemical Analysis of Neurotransmitters in Neurosecretory Protein GL-Producing Neurons of the Mouse Hypothalamus

We recently discovered a novel neuropeptide of 80 amino acid residues: neurosecretory protein GL (NPGL), in the hypothalamus of birds and rodents. NPGL is localized in the lateral posterior part of the arcuate nucleus (ArcLP), and it enhances feeding behavior and fat accumulation in mice. Various neurotransmitters, such as catecholamine, glutamate, and γ-aminobutyric acid (GABA), produced in the hypothalamus are also involved in energy metabolism. The colocalization of neurotransmitters and NPGL in neurons of the ArcLP leads to the elucidation of the regulatory mechanism of NPGL neurons. In this study, we performed double immunofluorescence staining to elucidate the relationship between NPGL and neurotransmitters in mice. The present study revealed that NPGL neurons did not co-express tyrosine hydroxylase as a marker of catecholaminergic neurons and vesicular glutamate transporter-2 as a marker of glutamatergic neurons. In contrast, NPGL neurons co-produced glutamate decarboxylase 67, a marker for GABAergic neurons. In addition, approximately 50% of NPGL neurons were identical to GABAergic neurons. These results suggest that some functions of NPGL neurons may be related to those of GABA. This study provides insights into the neural network of NPGL neurons that regulate energy homeostasis, including feeding behavior and fat accumulation.

Neurosecretory Protein GL Accelerates Liver Steatosis in Mice Fed Medium-Fat/Medium-Fructose Diet

Sugar consumption can readily lead to obesity and metabolic diseases such as liver steatosis. We previously demonstrated that a novel hypothalamic neuropeptide, neurosecretory protein GL (NPGL), promotes fat accumulation due to the ingestion of sugar by rats. However, differences in lipogenic efficiency of sugar types by NPGL remain unclear. The present study aimed to elucidate the obesogenic effects of NPGL on mice fed different sugars (i.e., sucrose or fructose). We overexpressed the NPGL-precursor gene (Npgl) in the hypothalamus of mice fed a medium-fat/medium-sucrose diet (MFSD) or a medium-fat/medium-fructose diet (MFFD). Food intake and body mass were measured for 28 days. Body composition and mRNA expression of lipid metabolic factors were measured at the endpoint. Npgl overexpression potently increased body mass with fat accumulation in the white adipose tissue of mice fed MFFD, although it did not markedly affect food intake. In contrast, we observed profound fat deposition in the livers of mice fed MFFD but not MFSD. In the liver, the mRNA expression of glucose and lipid metabolic factors was affected in mice fed MFFD. Hence, NPGL induced liver steatosis in mice fed a fructose-rich diet.

Hypothalamic Overexpression of Neurosecretory Protein GL Leads to Obesity in Male C57BL/6J Mice

INTRODUCTION

The mechanisms underlying obesity are not fully understood, necessitating the creation of novel animal models for the investigation of metabolic disorders. We have previously found that neurosecretory protein GL (NPGL), a newly identified hypothalamic neuropeptide, is involved in feeding behavior and fat accumulation in rats. However, the impact of NPGL on obesity remains unclear in any animal model. The present investigation sought to elucidate whether NPGL causes obesity in the obesity-prone mouse strain C57BL/6J.

METHODS

We overexpressed the NPGL-precursor gene (Npgl) in the hypothalamus using adeno-associated virus in male C57BL/6J mice fed normal chow (NC) or a high-calorie diet (HCD). After 9 weeks of Npgl overexpression, we measured adipose tissues, muscle, and several organ masses in addition to food intake and body mass. To assess the effects of Npgl overexpression on peripheral tissues, we analyzed mRNA expression of lipid metabolism-related genes by quantitative RT-PCR. Whole body energy consumption was assessed using an O2/CO2 metabolism measurement before an apparent increase in body mass.

RESULTS

Npgl overexpression increased food intake, body mass, adipose tissues and liver masses, and food efficiency under both NC and HCD, resulting in obesity observable within 8 weeks. Furthermore, we observed fat accumulation in adipose tissues and liver. Additionally, mRNA expression of lipid metabolism-related factors was increased in white adipose tissue and the liver after Npgl overexpression. Npgl overexpression inhibited energy expenditure during a dark period.

CONCLUSION

Taken together, the present study suggests that NPGL can act as an obesogenic factor that acts within a short period of time in mice. As a result, this Npgl overexpression-induced obesity can be widely applied to study the etiology of obesity from genes to behavior.

A Novel Hypothalamic Factor, Neurosecretory Protein GM, Causes Fat Deposition in Chicks

We recently discovered a novel cDNA encoding the precursor of a small secretory protein, neurosecretory protein GM (NPGM), in the mediobasal hypothalamus of chickens. Although our previous study showed that subcutaneous infusion of NPGM for 6 days increased body mass in chicks, the chronic effect of intracerebroventricular (i.c.v.) infusion of NPGM remains unknown. In this study, we performed i.c.v. administration of NPGM in eight-day-old layer chicks using osmotic pumps for 2 weeks. In the results, chronic i.c.v. infusion of NPGM significantly increased body mass, water intake, and the mass of abdominal and gizzard fat in chicks, whereas NPGM did not affect food intake, liver and muscle masses, or blood glucose concentration. Morphological analyses using Oil Red O and hematoxylin-eosin stainings revealed that fat accumulation occurred in both the liver and gizzard fat after NPGM infusion. The real-time PCR analysis showed that NPGM decreased the mRNA expression of peroxisome proliferator-activated receptor α, a lipolytic factor in the liver. These results indicate that NPGM may participate in fat storage in chicks.

Overexpression of the Gene Encoding Neurosecretory Protein GL Precursor Prevents Excessive Fat Accumulation in the Adipose Tissue of Mice Fed a Long-Term High-Fat Diet

We previously identified a novel small hypothalamic protein, neurosecretory protein GL (NPGL), which induces feeding behavior and fat accumulation in rodents depending on their diet. In the present study, we explored the effects of NPGL on feeding behavior and energy metabolism in mice placed on a long-term high-fat diet with 60% calories from fat (HFD 60). Overexpression of the NPGL precursor gene (Npgl) over 18 weeks increased food intake and weight. The weekly weight gain of Npgl-overexpressing mice was higher than that of controls until 7 weeks from induction of overexpression, after which it ceased to be so. Oral glucose tolerance tests showed that Npgl overexpression maintained glucose tolerance and increased blood insulin levels, and intraperitoneal insulin tolerance tests showed that it maintained insulin sensitivity. At the experimental endpoint, Npgl overexpression was associated with increased mass of the perirenal white adipose tissue (WAT) and decreased mass of the epididymal WAT (eWAT), resulting in little effect on the total WAT mass. These results suggest that under long-term HFD 60 feeding, Npgl overexpression may play a role in avoiding metabolic disturbance both by accelerating energy storage and by suppressing excess fat accumulation in certain tissues, such as the eWAT.

Effects of neurosecretory protein GL on food intake and fat accumulation under different dietary nutrient compositions in rats

We recently identified a novel hypothalamic small protein, named neurosecretory protein GL (NPGL), which is involved in energy homeostasis in birds and mammals. However, whether the action of NPGL is influenced by nutritional composition remains unknown. Thus, we investigated the effect of chronic intracerebroventricular infusion of NPGL for 13 days on feeding behavior and body mass gain under a normal chow (NC) diet, high-fat diet, high-sucrose diet (HSD), and medium-fat/medium-sucrose diet (MFSD) in rats. NPGL stimulated food intake of NC and MFSD, especially during the light period. By contrast, NPGL decreased body mass gain under NC and increased total white adipose tissue mass in HSD- and MFSD-fed rats. These data suggest that the effects of NPGL on feeding behavior, body mass gain, and fat accumulation depend on nutrient type. Among them, sucrose in diets seems to contribute to fat accumulation elicited by NPGL.

Subcutaneous infusion of neurosecretory protein GL promotes fat accumulation in mice

We recently identified a novel small secretory protein, neurosecretory protein GL (NPGL), in the vertebrate hypothalamus. We revealed that NPGL is involved in energy homeostasis using intracerebroventricular infusion in rodents. However, the effect of NPGL through peripheral administration remains to be elucidated and may be important for therapeutic use. In this study, we performed subcutaneous infusion of NPGL in mice for 12 days and found that it accelerated fat accumulation in white adipose tissue (WAT) without increasing in body mass gain and food intake. The mass of the testis, liver, kidney, heart, and gastrocnemius muscle remained unchanged. Analysis of mRNA expression by quantitative reverse transcription-polymerase chain reaction showed that proopiomelanocortin was suppressed in the hypothalamus by the infusion of NPGL. We observed a decreasing tendency in serum triglyceride levels due to NPGL, while serum glucose, insulin, leptin, and free fatty acids levels were unchanged. These results suggest that the peripheral administration of NPGL induces fat accumulation in WAT via the hypothalamus.

Effects of Overexpression of Neurosecretory Protein GL-Precursor Gene on Glucose Homeostasis and Insulin Sensitivity in Mice

A high-fat diet (HFD) quickly induces obesity with insulin resistance and hyperglycemia. We previously reported that a novel hypothalamic small protein, named neurosecretory protein GL (NPGL), stimulates feeding and fat accumulation in mice. However, the effects of NPGL on insulin sensitivity and glucose homeostasis remain unknown. Hence, we subjected NPGL-precursor gene (Npgl)-overexpressing mice to the oral glucose tolerance test (OGTT) and intraperitoneal insulin tolerance test (IPITT) under normal chow (NC) and HFD conditions. Npgl overexpression promoted body mass gain and tended to increase food intake of NC-fed mice, whereas it had little effect on HFD-fed mice. The OGTT showed elevated blood glucose and insulin levels in Npgl-overexpressing NC-fed mice 15 min after glucose administration. Both the OGTT and IPITT demonstrated that Npgl overexpression decreased blood glucose levels in HFD-fed mice 60 min after glucose and insulin treatments. Notably, Npgl overexpression increased adipose tissue masses only in NC-fed mice, and it decreased blood glucose and insulin levels in HFD-fed mice at the experimental end point. It also increased the mRNA expression of galanin, one of the feeding and metabolic regulatory neuropeptides, in the hypothalamus of HFD-fed mice. Therefore, NPGL may alleviate HFD-induced hyperglycemia and insulin resistance in mice.

Effects of Irregular Feeding on the Daily Fluctuations in mRNA Expression of the Neurosecretory Protein GL and Neurosecretory Protein GM Genes in the Mouse Hypothalamus

Circadian desynchrony induced by a long period of irregular feeding leads to metabolic diseases, such as obesity and diabetes mellitus. The recently identified neurosecretory protein GL (NPGL) and neurosecretory protein GM (NPGM) are hypothalamic small proteins that stimulate food intake and fat accumulation in several animals. To clarify the mechanisms that evoke feeding behavior and induce energy metabolism at the appropriate times in accordance with a circadian rhythm, diurnal fluctuations in Npgl and Npgm mRNA expression were investigated in mice. Quantitative RT-PCR analysis revealed that the mRNAs of these two genes were highly expressed in the mediobasal hypothalamus during the active dark phase under ad libitum feeding. In mice restricted to 3 h of feeding during the inactive light phase, the Npgl mRNA level was augmented in the moment prior to the feeding period and the midnight peak of Npgm mRNA was attenuated. Moreover, the mRNA expression levels of clock genes, feeding regulatory neuropeptides, and lipid metabolic enzymes in the central and peripheral tissues were comparable to those of central Npgl and Npgm. These data suggest that Npgl and Npgm transcription fluctuates daily and likely mediates feeding behavior and/or energy metabolism at an appropriate time according to the meal timing.

New insights into weight management by orlistat in comparison with cinnamon as a natural lipase inhibitor

BACKGROUND AND OBJECTIVES

Orlistat which is taken by obese patients may present some therapeutic assistance through its inhibition of lipase activity. Otherwise, a natural lipase inhibitor as cinnamon is widely used traditional medicine to decrease cholesterol and body weight. The current study aimed to investigate the weight management of orlistat in comparison with cinnamon through different obesity related targets.

METHODS

Subjects were divided into: Group 1: subjects received cinnamon capsules for 60 days. Group 2: subjects were received orlistat twice daily for 30 days, then once daily for another 30 days. Blood samples were collected at baseline and after 2 months.

RESULTS

Both orlistat and cinnamon groups showed a significant reduction in BMI, lipid profile, and lipase activity compared with baseline. Orlistat group showed significant elevation (p < 0.001) in glucagon, insulin-degrading enzyme (IDE) and dopamine level concomitant with the decrease of serum glutamate compared with baseline level of the same group and cinnamon group. However, cinnamon reduced serum insulin level and insulin resistance (IR) compared with baseline level of the same group and orlistat group.

CONCLUSIONS

Orlistat can be used in weight management not only for its pancreatic lipase inhibition but also, due to its indirect appetite reduction effect through elevated glucagon, IDE and dopamine levels and its inhibitory effect on glutamate neurotransmitter, whereas, cinnamon improves BMI and glycaemic targets.

Neurosecretory Protein GL Induces Fat Accumulation in Chicks

We recently found a previously unidentified cDNA in chicken hypothalamus which encodes the precursor for neurosecretory protein GL (NPGL). A previous study showed that intracerebroventricular (i.c.v.) infusion of NPGL caused body mass gain in chicks. However, it was not clear which part(s) of the body gained mass. In the present study, we investigated which tissues increased in mass after chronic i.c.v. infusion of NPGL in chicks. We found that NPGL increased the masses of the liver, abdominal fat, and subcutaneous fat, while NPGL did not affect the masses of muscles, including pectoralis major, pectoralis minor, and biceps femoris. Oil Red O staining revealed that fat deposition had occurred in the liver. In addition, the size of the lipid droplets in the abdominal fat increased. Furthermore, we found an upregulation of lipogenesis and downregulation of lipolysis in the abdominal fat, but not in the liver. These results indicate that NPGL is involved in fat storage in chicks.

nNOS immunoreactivity co-localizes with GABAergic and cholinergic neurons, and associates with β-endorphinergic and met-enkephalinergic opioidergic fibers in rostral ventromedial medulla and A5 of the mouse

The present study examined the co-expression of neuronal nitric oxide synthase (nNOS) in the rostral ventromedial medulla (RVM) and A5 regions of the mouse brainstem within several neurochemical populations involved in nociceptive modulation. Double immunohistochemical methods showed that nNOS+ neurons do not co-localize with serotonergic neurons within any of these regions. Within the RVM, the nuclei raphe magnus and gigantocellularis contain a population of nNOS+/GAD67+ neurons, and within the paragigantocellularis lateralis, there is a smaller population of nNOS+/CHAT+ neurons. Further, nNOS+ neurons overlap the region of expression of β-endorphinergic and met-enkephalinergic fibers within the RVM. No co-labeling was found within the A5 for any of these populations. These findings suggest that pain-modulatory serotonergic neurons within the brainstem do not directly produce nitric oxide (NO). Rather, NO-producing neurons within the RVM belong to GABAergic and cholinergic cell populations, and are in a position to modulate or be modulated by local opioidergic neurons.

Chronic subcutaneous infusion of neurosecretory protein GM increases body mass gain in chicks

Recently we discovered a small hypothalamic protein in the chicken, named neurosecretory protein GL (NPGL), which is associated with body growth and energy metabolism in birds and rodents. Genome database analysis suggested that the NPGL gene has a paralogous gene in vertebrates, named neurosecretory protein GM (NPGM). However, the biological action of NPGM remains unclear. In this study, we investigated whether NPGM affects body growth in chicks. We found that subcutaneous infusion of NPGM for six days increased body mass gain in a dose-dependent manner. Despite the observed increase in body mass, infusion of NPGM did not alter food and water intake. Of note, we observed tendency of mass increase of several peripheral tissues, specifically. When we compared several tissue types, NPGM seemed to induce the largest growth increase in white adipose tissue mass. These results suggest that NPGM may accelerate fat accumulation and body growth. In addition, we analyzed whether NPGM increases body growth through the action of pituitary hormones. However, we observed no significant changes in mRNA expression of pituitary hormones or plasma levels of growth hormone in NPGM-treated chicks. This is the first report describing the biological action of NPGM in vertebrates.

Avian and murine neurosecretory protein GL participates in the regulation of feeding and energy metabolism

Probing previously unknown neuropeptides and/or peptide hormones is essential for our understanding of the regulation of energy homeostasis in the brain. We recently performed a cDNA subtractive screening of the chicken hypothalamus, which contained one of the feeding and energy metabolic centers. We found a gene encoding a novel protein of 182 amino acid residues, including one putative small secretory protein of 80 amino acid residues. The C-terminal amino acids of the small protein were Gly-Leu-NH₂, and as a result, the small protein was termed neurosecretory protein GL (NPGL). Subcutaneous and intracerebroventricular infusions of NPGL increased body mass gain in chicks, suggesting a central role for this protein in regulating growth and energy homeostasis. A database search revealed that the Npgl gene is conserved in vertebrates, including mice and rats. This review summarizes the advances in the characterization, localization, and biological action of NPGL, in birds and rodents.

Localization and function of neurosecretory protein GM, a novel small secretory protein, in the chicken hypothalamus

Recently, we discovered a novel cDNA encoding the precursor of a small secretory protein, neurosecretory protein GL (NPGL), in the hypothalamic infundibulum of chickens. NPGL plays an important role in the regulation of growth and feeding. A database search indicated that the NPGL gene has a paralogous gene: neurosecretory protein GM (NPGM), also in chickens. We identified cDNA encoding the NPGM precursor in chickens. Morphological analysis showed that NPGM-containing cells are specifically localized in the medial mammillary nucleus (MM) and infundibular nucleus (IN) in the hypothalamus. In addition, we found that NPGM and NPGL are co-localized, especially in the MM. The expression levels of NPGM mRNA gradually decreased during post-hatch development, in contrast to those of NPGL mRNA. Moreover, we investigated the relationship between NPGM and other known factors. NPGM was found to be produced in histaminergic neurons in the MM. NPGM and histidine decarboxylase, a histamine-producing enzyme, displayed similar expression patterns during post-hatch development. Acute intracerebroventricular injection of NPGM decreased food intake, similar to the effect of histamine. To our knowledge, this is the first report of the localization and function of NPGM in the brain of vertebrates. These results will further advance the understanding mechanisms underlying energy homeostasis.

Neurosecretory protein GL stimulates food intake, de novo lipogenesis, and onset of obesity

Mechanisms underlying the central regulation of food intake and fat accumulation are not fully understood. We found that neurosecretory protein GL (NPGL), a newly-identified neuropeptide, increased food intake and white adipose tissue (WAT) in rats. NPGL-precursor gene overexpression in the hypothalamus caused increases in food intake, WAT, body mass, and circulating insulin when fed a high calorie diet. Intracerebroventricular administration of NPGL induced de novo lipogenesis in WAT, increased insulin, and it selectively induced carbohydrate intake. Neutralizing antibody administration decreased the size of lipid droplets in WAT. Npgl mRNA expression was upregulated by fasting and low insulin levels. Additionally, NPGL-producing cells were responsive to insulin. These results point to NPGL as a novel neuronal regulator that drives food intake and fat deposition through de novo lipogenesis and acts to maintain steady-state fat level in concert with insulin. Dysregulation of NPGL may be a root cause of obesity.

DOI:http://dx.doi.org/10.7554/eLife.28527.001

Throughout history, our ancestors needed to accumulate fat to survive during times when food sources were scarce. However, for most people in the modern age, food is abundant and eating too much is a major cause of weight gain, obesity and diseases affecting the metabolism. Obesity in particular, can lead to diseases such as diabetes and heart disease.

Hunger and appetite are regulated by proteins and other chemicals that act as messengers, for example insulin, and a region of the brain called the hypothalamus. However, the full mechanisms that regulate these sensations remain unclear. Only recently, a protein called NPGL was discovered in a part of the hypothalamus of birds and mammals. However, it was not known if NPGL plays a role in regulating eating habits and weight gain.

Iwakoshi-Ukena et al. have now discovered that NPGL is found in the hypothalamus of rats and is regulated by diet and insulin. When the gene for NPGL was manipulated to produce too much of the protein, rats fed a high calorie diet started to eat more, and gained more weight and body fat. Adding additional NPGL to their brains had the same effect. When the animals were fed a normal diet, NPGL only moderately affected how much they ate, but it substantially increased how much fat they produced. Iwakoshi-Ukena et al. also observed that when animals were starved and insulin levels were low, the rats started to produce more NPGL. These results suggest that NPGL plays a role in fat storage when energy sources are limited, and can contribute to obesity when too much NPGL is produced in animals on a high calorie diet.

These findings indicate that NPGL could be an additional brain chemical that regulates hunger and fat storage in mammals. A next step will be to reveal the specific mechanisms by which NPGL regulates overeating and fat accumulation. These findings will further advance the study and treatment of obesity and obesity-related diseases.

DOI:http://dx.doi.org/10.7554/eLife.28527.002