Glucose homeostasis is impaired in mice deficient in the neuropeptide 26RFa (QRFP)

INTRODUCTION

26RFa (pyroglutamyl RFamide peptide (QRFP)) is a biologically active peptide that has been found to control feeding behavior by stimulating food intake, and to regulate glucose homeostasis by acting as an incretin. The aim of the present study was thus to investigate the impact of 26RFa gene knockout on the regulation of energy and glucose metabolism.

RESEARCH DESIGN AND METHODS

26RFa mutant mice were generated by homologous recombination, in which the entire coding region of prepro26RFa was replaced by the iCre sequence. Energy and glucose metabolism was evaluated through measurement of complementary parameters. Morphological and physiological alterations of the pancreatic islets were also investigated.

RESULTS

Our data do not reveal significant alteration of energy metabolism in the 26RFa-deficient mice except the occurrence of an increased basal metabolic rate. By contrast, 26RFa mutant mice exhibited an altered glycemic phenotype with an increased hyperglycemia after a glucose challenge associated with an impaired insulin production, and an elevated hepatic glucose production. Two-dimensional and three-dimensional immunohistochemical experiments indicate that the insulin content of pancreatic β cells is much lower in the 26RFa^-/- mice as compared with the wild-type littermates.

CONCLUSION

Disruption of the 26RFa gene induces substantial alteration in the regulation of glucose homeostasis, with in particular a deficit in insulin production by the pancreatic islets. These findings further support the notion that 26RFa is an important regulator of glucose homeostasis.

Acute but Not Chronic Central Administration of the Neuropeptide 26RFa (QRFP) Improves Glucose Homeostasis in Obese/Diabetic Mice

INTRODUCTION

The aim of the study is to investigate whether acute or chronic central administration of the hypothalamic neuropeptide 26RFa may ameliorate the glycemic control of obese/diabetic mice.

METHODS

Mice were treated for 4 months with a high-fat (HF) diet and received a single i.c.v. injection of 26RFa (3 µg) or a chronic i.c.v. administration of the peptide during 28 days via osmotic minipumps (25 µg/day). i.p. and oral glucose (GLU) tolerance tests, insulin (INS) tolerance test, glucose-stimulated insulin secretion (GSIS), food/water intake, horizontal/vertical activity, energy expenditure, meal pattern, and whole-body composition were monitored. In addition, 26RFa and GPR103 mRNA expressions as well as plasma 26RFa levels were evaluated by RT-QPCR and radioimmunoassay.

RESULTS

Acute administration of 26RFa in HF mice induced a robust antihyperglycemic effect by enhancing INS secretion, whereas chronic administration of the neuropeptide is unable to improve glucose homeostasis in these obese/diabetogenic conditions. By contrast, chronic 26RFa treatment induced an increase of the body weight accompanied with an enhanced food intake and a decreased energy expenditure. Finally, we show that the HF diet does not alter the hypothalamic expression of the 26RFa/GPR103 neuropeptidergic system nor the levels of circulating 26RFa.

CONCLUSION

Our data indicate that the central beneficial effect of 26RFa on glucose homeostasis, by potentiating GSIS, is preserved in HF mice. However, chronic administration of the neuropeptide is unable to balance glycemia in these pathophysiological conditions, suggesting that the hypothalamic 26RFa/GPR103 neuropeptidergic system mainly affects short-term regulation of glucose metabolism.

Blood Levels of Neuropeptide 26RFa in Relation to Anxiety and Aggressive Behavior in Humans-An Exploratory Study

26RFa, also referred to as QRFP, is a hypothalamic neuropeptide mainly known for its role in the regulation of appetite and glucose metabolism. Its possible relevance to emotional regulation is largely unexplored. To address this, in the present exploratory study, we analyzed the plasma concentrations of 26RFa in humans characterized by different levels of anxiety and aggressive behavior. For this purpose, the study included 13 prison inmates who have committed violent crimes and 19 age-matched healthy men from the general population as controls. Anxiety, depression and aggressive behavior were evaluated in both groups using standard questionnaires. The inmate group was characterized by increased aggression and anxiety compared to the controls. We found that the mean plasma levels of 26RFa did not significantly differ between the inmates and the controls. However, several high outliers were present only in the inmate group. The plasma levels of 26RFa correlated positively with the anxiety scores in all the studied subjects and controls. After removing the high outliers in the inmate group, positive correlations of 26RFa with anxiety and a subscale of hostility in the aggression scale were also recorded in this group. No significant correlations of 26RFa with depression scores or other parameters of aggressive behavior were found. Thus, the present results did not support an involvement of 26RFa in aggressive behavior in humans but pointed to a link between this neuropeptide and anxiety. Nevertheless, considering the exploratory nature of the present study, this conclusion should be verified in a larger cohort, including the clinical degree of anxiety.

Immunoglobulin G is a natural oxytocin carrier which modulates oxytocin receptor signaling: relevance to aggressive behavior in humans

Oxytocin is a neuropeptide produced mainly in the hypothalamus and secreted in the CNS and blood. In the brain, it plays a major role in promoting social interactions. Here we show that in human plasma about 60% of oxytocin is naturally bound to IgG which modulates oxytocin receptor signaling. Further, we found that IgG of violent aggressive inmates were characterized by lower affinity for oxytocin, causing decreased oxytocin carrier capacity and reduced receptor activation as compared to men from the general population. Moreover, peripheral administration of oxytocin together with human oxytocin-reactive IgG to resident mice in a resident-intruder test, reduced c-fos activation in several brain regions involved in the regulation of aggressive/defensive behavior correlating with the attack number and duration. We conclude that IgG is a natural oxytocin carrier protein modulating oxytocin receptor signaling which can be relevant to the biological mechanisms of aggressive behavior.

The 26RFa (QRFP)/GPR103 neuropeptidergic system in mice relays insulin signalling into the brain to regulate glucose homeostasis

AIMS/HYPOTHESIS

26RFa (pyroglutamilated RFamide peptide [QRFP]) is a biologically active peptide that regulates glucose homeostasis by acting as an incretin and by increasing insulin sensitivity at the periphery. 26RFa is also produced by a neuronal population localised in the hypothalamus. In this study we investigated whether 26RFa neurons are involved in the hypothalamic regulation of glucose homeostasis.

METHODS

26Rfa^+/+, 26Rfa^-/- and insulin-deficient male C57Bl/6J mice were used in this study. Mice received an acute intracerebroventricular (i.c.v.) injection of 26RFa, insulin or the 26RFa receptor (GPR103) antagonist 25e and were subjected to IPGTTs, insulin tolerance tests, acute glucose-stimulated insulin secretion tests and pyruvate tolerance tests (PTTs). Secretion of 26RFa by hypothalamic explants after incubation with glucose, leptin or insulin was assessed. Expression and quantification of the genes encoding 26RFa, agouti-related protein, the insulin receptor and GPR103 were evaluated by quantitative reverse transcription PCR and RNAscope in situ hybridisation.

RESULTS

Our data indicate that i.c.v.-injected 26RFa induces a robust antihyperglycaemic effect associated with an increase in insulin production by the pancreatic islets. In addition, we found that insulin strongly stimulates 26Rfa expression and secretion by the hypothalamus. RNAscope experiments revealed that neurons expressing 26Rfa are mainly localised in the lateral hypothalamic area, that they co-express the gene encoding the insulin receptor and that insulin induces the expression of 26Rfa in these neurons. Concurrently, the central antihyperglycaemic effect of insulin is abolished in the presence of a GPR103 antagonist and in 26RFa-deficient mice. Finally, our data indicate that the hypothalamic 26RFa neurons are not involved in the central inhibitory effect of insulin on hepatic glucose production, but mediate the central effects of the hormone on its own peripheral production.

CONCLUSION/INTERPRETATION

We have identified a novel mechanism in the hypothalamic regulation of glucose homeostasis, the 26RFa/GPR103 system, and we provide evidence that this neuronal peptidergic system is a key relay for the central regulation of glucose metabolism by insulin.

Long-Term Dynamics of Serum α-MSH and α-MSH-Binding Immunoglobulins with a Link to Gut Microbiota Composition in Patients with Anorexia Nervosa

INTRODUCTION

Immunoglobulins (Ig) reactive with α-melanocyte-stimulating hormone (α-MSH), an anorexigenic neuropeptide, are present in humans and were previously associated with eating disorders. In this longitudinal study involving patients with anorexia nervosa (AN), we determined whether α-MSH in serum is bound to IgG and analyzed long-term dynamics of both α-MSH peptide and α-MSH-reactive Ig in relation to changes in BMI and gut microbiota composition.

METHODS

The study included 64 adolescents with a restrictive form of AN, whose serum samples were collected at hospital admission, discharge, and during a 1-year follow-up visit and 41 healthy controls, all females.

RESULTS

We found that in both study groups, approximately 40% of serum α-MSH was reversibly bound to IgG and that levels of α-MSH-reactive IgG but not of α-MSH peptide in patients with AN were low at hospital admission but recovered 1 year later. Total IgG levels were also low at admission. Moreover, BMI-standard deviation score correlated positively with α-MSH IgG in both groups studied but negatively with α-MSH peptide only in controls. Significant correlations between the abundance of specific bacterial taxa in the gut microbiota and α-MSH peptide and IgG levels were found in both study groups, but they were more frequent in controls.

CONCLUSION

We conclude that IgG in the blood plays a role as an α-MSH-binding protein, whose characteristics are associated with BMI in both patients with AN and controls. Furthermore, the study suggests that low production of α-MSH-reactive IgG during the starvation phase in patients with AN may be related to altered gut microbiota composition.

Interactions between the regulatory peptide 26RFa (QRFP) and insulin in the regulation of glucose homeostasis in two complementary models: The high fat 26RFa-deficient mice and the streptozotocin insulin-deficient mice

The regulatory peptide 26RFa (QRFP) is involved in the control of glucose homeostasis at the periphery by acting as an incretin, and in the brain by mediating the central antihyperglycemic effect of insulin, indicating the occurrence of a close relationship between 26RFa and insulin in the regulation of glucose metabolism. Here, we investigated the physiological interactions between 26RFa and insulin in two complementary models i.e. a model of obese/hyperglycemic mice deficient for 26RFa and a model of diabetic mice deficient for insulin. For this, transgenic 26RFa-deficient mice were made obese and chronically hyperglycemic by a 3-month high fat diet (HFD) and second group of mice was made diabetic by destruction of the β cells of the pancreatic islets using a single injection of streptozotocin. Our data reveal that 26RFa deficiency does not impact significantly the "glycemic" phenotype of the HFD mice. The pancreatic islets, liver, white adipose tissue masses are not altered by the lack of 26RFa production but the brown adipose tissue (BAT) weight is significantly increased in these animals. In diabetic insulin-deficient mice, the injection of 26RFa does not exhibit any beneficial effect on the impaired glucose homeostasis characterizing this model. Finally, we show that streptozotocin diabetic mice display lowered plasma 26RFa levels as compared to untreated mice, whereas the expression of the peptide in the duodenum is not affected. Taken together, the present results indicate that dysregulation of glucose homeostasis in obese/hyperglycemic mice is not aggravated by the absence of 26RFa that may be compensated by the increase of BAT mass. In diabetic insulin-deficient mice, the antihypergycemic effect of 26RFa is totally blunted probably as a result of the impaired insulin production characterizing this model, avoiding therefore the action of the peptide.

The 26RFa (QRFP)/GPR103 Neuropeptidergic System: A Key Regulator of Energy and Glucose Metabolism

BACKGROUND

Obesity and type 2 diabetes are strongly associated pathologies, currently considered as a worldwide epidemic problem. Understanding the mechanisms that drive the development of these diseases would enable to develop new therapeutic strategies for their prevention and treatment. Particularly, the role of the brain in energy and glucose homeostasis has been studied for 2 decades. In specific, the hypothalamus contains well-identified neural networks that regulate appetite and potentially also glucose homeostasis. A new concept has thus emerged, suggesting that obesity and diabetes could be due to a dysfunction of the same, still poorly understood, neural networks.

SUMMARY

The neuropeptide 26RFa (also termed QRFP) belongs to the family of RFamide regulatory peptides and has been identified as the endogenous ligand of the human G protein-coupled receptor GPR103 (QRFPR). The primary structure of 26RFa is strongly conserved during vertebrate evolution, suggesting its crucial roles in the control of vital functions. Indeed, the 26RFa/GPR103 peptidergic system is reported to be involved in the control of various neuroendocrine functions, notably the control of energy metabolism in which it plays an important role, both centrally and peripherally, since 26RFa regulates feeding behavior, thermogenesis and lipogenesis. Moreover, 26RFa is reported to control glucose homeostasis both peripherally, where it acts as an incretin, and centrally, where the 26RFa/GPR103 system relays insulin signaling in the brain to control glucose metabolism.

KEY MESSAGES

This review gives a comprehensive overview of the role of the 26RFa/GPR103 system as a key player in the control of energy and glucose metabolism. In a pathophysiological context, this neuropeptidergic system represents a prime therapeutic target whose mechanisms are highly relevant to decipher.

Glucose and energy metabolism are impaired in mice deficient for orexins

Graphical abstract

Abstract

The present study aims to investigate the impact of orexin deficiency on the regulation of energy and glucose metabolism using a mouse model depleted of the prepro-orexin gene. Our data reveal that, despite a decrease in food consumption (at least in males), orexin deficiency induces a significant increase in body weight that is associated with an alteration in the body composition, as male and female orexin-deficient mice display increased fat mass compared to wild-type littermates. Nevertheless, no significant differences of global energy expenditure and locomotor activity were observed in the mutant mice relative to the control. Glucose homeostasis is also impaired in the absence of orexins, since glucose tolerance and insulin secretion are diminished, and insulin sensitivity is slightly reduced. In addition, the livers of male orexin-KO mice are significantly larger and heavier with more adipose tissue than wild-type mice. Interestingly, orexin-deficient mice present an upregulation of liver enzymes involved in gluconeogenesis and a downregulation of GCK, an enzyme that promotes glycogen storage, which may participate to the altered glucose metabolism of orexin mutant mice. To conclude, the present study indicates that orexin deficiency induces profound alterations in the regulation of energy and glucose metabolism, which is more pronounced in males than in females. These findings support the idea that dysfunction of this orexin system may promote obesity and diabetes, and could represent an interesting therapeutic target in the context of 'diabesity'.

Serum levels of the incretin-like peptide 26RFa are diminished in women living with obesity and diabetes and restored after sleeve gastrectomy: Results from the prospective pilot RFa-Ba-S study

AIM

To investigate the evolution of the incretin-like peptide 26RFa in a prospective cohort of women living with obesity with or without type 2 diabetes (T2D) before and after sleeve gastrectomy (SG).

METHODS

In this study, a total of 61 women were divided into three groups: women living with severe obesity without T2D (WlwOB group), women living with severe obesity and T2D (WlwOB-T2D group) and lean healthy volunteers (control group). Serum 26RFa concentrations were measured using a 26RFa enzyme-linked immunosorbent assay developed specifically for this study during meal tests before SG, and 30 and 180 days after SG.

RESULTS

At baseline, serum 26RFa levels were reduced in the WlwOB (P < .05) and WlwOB-T2D (P < .01) groups compared with controls. In the WlwOB-T2D group, fasting 26RFa levels were found to increase throughout the entire follow-up period up to 6 months after the SG (P < .001). During the meal tests, serum 26RFa levels increased, especially in the WlwOB-T2D group at baseline. At the end of the follow-up, the profile of 26RFa concentrations obtained during the meal test in patients with severe obesity and T2D was similar to that of the controls.

CONCLUSIONS

This prospective clinical study provides the first evidence that circulating 26RFa is altered mainly in WlwOB-T2D, and that these defects are partially reversed after SG.