26RFa

Hypothalamic Neuropeptide 26RFa Acts as an Incretin to Regulate Glucose Homeostasis.[Pubmed:25858563]

Diabetes. 2015 Aug;64(8):2805-16.

26RFa is a hypothalamic neuropeptide that promotes food intake. 26RFa is upregulated in obese animal models, and its orexigenic activity is accentuated in rodents fed a high-fat diet, suggesting that this neuropeptide might play a role in the development and maintenance of the obese status. As obesity is frequently associated with type 2 diabetes, we investigated whether 26RFa may be involved in the regulation of glucose homeostasis. In the current study, we show a moderate positive correlation between plasma 26RFa levels and plasma insulin in patients with diabetes. Plasma 26RFa concentration also increases in response to an oral glucose tolerance test. In addition, we found that 26RFa and its receptor GPR103 are present in human pancreatic beta-cells as well as in the gut. In mice, 26RFa attenuates the hyperglycemia induced by a glucose load, potentiates insulin sensitivity, and increases plasma insulin concentrations. Consistent with these data, 26RFa stimulates insulin production by MIN6 insulinoma cells. Finally, we show, using in vivo and in vitro approaches, that a glucose load induces a massive secretion of 26RFa by the small intestine. Altogether, the present data indicate that 26RFa acts as an incretin to regulate glucose homeostasis.

Anxiolytic effect of the GPR103 receptor agonist peptide P550 (homolog of neuropeptide 26RFa) in mice. Involvement of neurotransmitters.[Pubmed:27224020]

Peptides. 2016 Aug;82:20-25.

The GPR103 receptor is a G protein-coupled receptor, which plays a role in several physiological functions. However, the role of the GPR103 receptor in anxiety has not been clarified. The first aim of our study was to elucidate the involvement of the GPR103 receptor in anxious behavior. Mice were treated with peptide P550, which is the mouse homolog of neuropeptide 26RFa and has similar activity for the GPR103 receptor as neuropeptide 26RFa. The anxious behavior was investigated using an elevated plus-maze paradigm. The second aim of our study was to investigate the underlying neurotransmissions. Accordingly, mice were pretreated with a nonselective muscarinic acetylcholine receptor antagonist, atropine, a gamma-aminobutyric acid subunit A (GABAA) receptor antagonist, bicuculline, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist, methysergide, a D2, D3, D4 dopamine receptor antagonist, haloperidol, a nonselective alpha-adrenergic receptor antagonist, phenoxybenzamine and a nonselective beta-adrenergic receptor antagonist, propranolol. Our results demonstrated that peptide P550 reduces anxious behavior in elevated plus maze test in mice. Our study shows also that GABAA-ergic, alpha- and beta-adrenergic transmissions are all involved in this action, whereas 5-HT1 and 5-HT2 serotonergic, muscarinic cholinergic and D2, D3, D4 dopaminergic mechanisms may not be implicated.

The Neuropeptide 26RFa (QRFP) and Its Role in the Regulation of Energy Homeostasis: A Mini-Review.[Pubmed:27965532]

Front Neurosci. 2016 Nov 29;10:549.

This mini-review deals with the neuropeptide 26RFa (or QRFP) which is a member of the RFamide peptide family discovered simultaneously by three groups in 2003. 26RFa (or its N-extended form 43RFa) was subsequently shown to be the endogenous ligand of the human orphan receptor GPR103. In the brain, 26RFa and GPR103mRNA are primarily expressed in hypothalamic nuclei involved in the control of feeding behavior, and at the periphery, the neuropeptide and its receptor are present in abundance in the gut and the pancreatic islets, suggesting that 26RFa is involved in the regulation of energy metabolism. Indeed, 26RFa stimulates food intake when injected centrally, and its orexigenic effect is even more pronounced in obese animals. The expression of 26RFa is up-regulated in the hypothalamus of obese animals, supporting that the 26RFa/GPR103 system may play a role in the development and/or maintenance of the obese status. Recent data indicate that 26RFa is also involved in the regulation of glucose homeostasis. 26RFa reduces glucose-induced hyperglycemia, increases insulin sensitivity and insulinemia. Furthermore, an oral ingestion of glucose strongly stimulates 26RFa release by the gut, indicating that 26RFa is a novel incretin. Finally, 26RFa is able to prevent pancreatic beta cell death and apoptosis. This brief overview reveals that 26RFa is a key neuropeptide in the regulation of energy metabolism. Further fields of research are suggested including the pathophysiological implication of the 26RFa/GPR103 system.

[The neuropeptide 26RFa and its role in the regulation of energy metabolism].[Pubmed:28327281]

Biol Aujourdhui. 2016;210(4):227-235.

The neuropeptide 26RFa, also referred to as QRFP (for pyroglutamilated RFamide peptide), is the latest member of the RFamide peptide family to be discovered. 26RFa and its N-extended form, 43RFa, have been characterized in all vertebrate classes as the endogenous ligands of the human orphan receptor GPR103. In the brain, 26RFa and GPR103mRNA are primarily expressed in hypothalamic nuclei involved in the control of feeding behavior, and in the periphery, the neuropeptide and its receptor are present in abundance in the gut and the pancreatic islets, suggesting that 26RFa is involved in the regulation of energy metabolism. Indeed, 26RFa stimulates food intake when centrally injected, and its orexigenic effect is even more pronounced in obese animals. The expression of 26RFa is up-regulated in the hypothalamus of obese animals, supporting the view that 26RFa may play a role in the development and/or maintenance of the obese status. Recent data indicate that 26RFa is also involved in the regulation of glucose homeostasis. 26RFa reduces glucose-induced hyperglycemia, increases insulin sensitivity and insulinemia. Furthermore, an oral ingestion of glucose strongly stimulates 26RFa release by the gut, indicating that 26RFa is a novel incretin. Finally, 26RFa is able to prevent pancreatic beta cell death and apoptosis. In conclusion, this overview of the literature reveals that 26RFa is a key neuropeptide in the regulation of energy metabolism. Further fields of research are suggested including the pathophysiological implication of the 26RFa/GPR103 system.

Structure-activity relationships of a series of analogues of the RFamide-related peptide 26RFa.[Pubmed:21623631]

J Med Chem. 2011 Jul 14;54(13):4806-14.

26RFa is a new member of the RFamide peptide family that has been identified as the endogenous ligand of the orphan GPCR GPR103. As the C-terminal heptapeptide (26RFa((20-26))) mimics the action of the native peptide on food intake and gonadotropin secretion in rodents, we have synthesized a series of analogues of 26RFa((20-26)) and measured their potency to induce [Ca(2+)](i) mobilization in Galpha(16)-hGPR103-transfected CHO cells. Systematic replacement of each residue by an alanine (Ala scan) and its D-enantiomer (D scan) showed that the last three C-terminal residues were very sensitive to the substitutions while position 23 tolerated rather well both modifications. Most importantly, replacement of Ser(23) by a norvaline led to an analogue, [Nva(23)]26RFa((20-26)), that was 3-fold more potent than the native heptapeptide. These new pharmacological data, by providing the first information regarding the structure-activity relationships of 26RFa analogues, should prove useful for the rational design of potent GPR103 receptor ligands with potential therapeutic application.

Effect of central administration of QRFP(26) peptide on energy balance and characterization of a second QRFP receptor in rat.[Pubmed:16996040]

Brain Res. 2006 Nov 13;1119(1):133-49.

The recently identified neuropeptide QRFP(26) is predominantly expressed in the hypothalamus and was suggested to play a role in the regulation of food intake following the observation of an acute orexigenic effect after central administration in mice. QRFP(26) exerts its effect via GPR103 and a newly identified receptor in mouse. The aim of our study was (a) to investigate the distribution of QRFP(26) and a newly discovered QRFP receptor mRNA in rat and (b) to further characterize the effects of central administration of QRFP(26) on energy balance in rats. QRFP(26) mRNA was detected in the retrochiasmatic nucleus, periventricular nucleus, arcuate nucleus and restricted areas of the lateral nucleus of the hypothalamus. We found an additional receptor with high homology for GPR103 in rat. This receptor increases inositol triphosphate production in transfected cells in presence of QRFP(26) and its mRNA was particularly enriched in ventral and posterior thalamic groups, anterior hypothalamus and medulla. When QRFP(26) (10 microg and 50 microg) was administered centrally before the start of the light phase both doses increased food intake for 2 h after injection without reaching statistical significance. QRFP(26) caused no changes in locomotor activity or energy expenditure. In summary, central QRFP(26) injection causes slight and transient hyperphagia in rats without changing any other energy balance parameters after 24 h. We conclude that QRFP(26) has limited impact on the central regulation of energy balance in rats and that its essential function remains to be clarified.