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

Abstract

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/interpretationWe 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.

Structure basis for recognition of 26RFa by the pyroglutamylated RFamide peptide receptor

“…3b). Alanine substitution of W111 23,50 and two conserved cysteines notably hamper QRFPR activation (Fig. 3d), which coincides with the non-detectable activity of the C-terminal heptapeptide when substituting Phe24 with alanine or D-Phe 21 .…”

“…They moderately impact 26RFa activity, as substituting these two glycines of C-terminal heptapeptide with a bulkier alanine reduced the potency of 26RFa (20-26) by 4-5 folds 21 . The side chain of Phe22 forms an intramolecular hydrophobic interaction with Phe24, which makes an extensive hydrophobic network V101 2,60 , P122 3,29 , W111 23,50 , and the conserved disulfide bond between C118 3,25 and C201 45,50 (Fig. 3b).…”

“…The amino acid sequences of 26RFa are conserved among mammalian species 20 , with 26RFa from rats being slightly more potent than that from humans in calcium mobilization 21 . Upon activating by 26RFa, QPFPR couples to G q and G i/o proteins 18,17 and regulates a wide range of physiological functions, such as promoting sleep in zebrafish 22 , increasing food intake 7 and insulin sensitivity 23 , modulating aldosterone secretion 24 , regulating bone formation 19 , and nociceptive transmission 25 in rodent. Selective agonists and antagonists of QRFPR may take effect in the treatment of metabolic imbalance (obesity, diabetes), eating disorders, and osteoporosis.…”

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

“…Indeed, several earlier studies showed that 26RFa has a central orexigenic effect [8]. Moreover, 26RFa plays a key role in mediating the hypoglycemic effect of insulin in the brain [9]. Hypothalamic expression of 26RFa, in particular in the VMH region, which harbors the 'aggression center' in the ventrolateral part of the ventromedial nucleus (VMN) [10], suggests that it may also be relevant to aggressive behavior.…”

Emerging role of UFMylation in secretory cells involved in the endocrine system by maintaining ER proteostasis

“…Compared with other endocrine hormones that are ultimately guided by the pituitary gland, the pancreatic beta cell is unique in its capacity to synthesize, store and secrete insulin with precise rates in response to circulating sugar, covering the metabolic needs of the organism ( 86 ). The fine-tuning of insulin production and secretion is modulated at multiple levels, ranging from transcription, mRNA stability to translation and protein folding.…”