Elsevier

Peptides

Volume 27, Issue 11, November 2006, Pages 2715-2721
Peptides

Behavioral effects of 26RFamide and related peptides

https://doi.org/10.1016/j.peptides.2006.04.017Get rights and content

Abstract

A novel 26-amino acid peptide possessing the Arg–Phe–NH2 motif at its C-terminal extremity has been recently characterized and named 26RFamide (26RFa). The 26RFa precursor encompasses several potential cleavage sites and thus may generate various mature peptides including an N-terminally extended form of 26RFa (termed 43RFa), two fragments of 26RFa (26RFa1–16 and 26RFa20–26), and a 9-amino acid peptide (9RFa) located in tandem in the human 26RFa precursor. In the present study, we have investigated the central effects of 26RFa and related peptides on food intake and locomotor activity in mice. We observed that i.c.v. injection of 26RFa, 43RFa, 26RFa20–26 and 9RFa stimulated food consumption while 26RFa1–16 and 26RFa8–16 had no effect. A dose-dependent stimulation of locomotor activity was observed after i.c.v. administration of 26RFa, 43RFa and 26RFa1–16, but not 26RFa20–26, 26RFa8–16 or 9RFa. These data indicate that the novel neuropeptides 26RFa and 43RFa act centrally to stimulate feeding and locomotor activities but the domains of the peptide involved in each of these responses are different suggesting that the two behavioral effects may be mediated through distinct receptors.

Introduction

The term RFamide–related peptides (RFRPs) designates a family of biologically active peptides that possess the motif Arg–Phe–NH2 at their C-terminal extremity [6]. The first member of this family, the tetrapeptide H–Phe–Met–Arg–Phe–NH2, was originally isolated from the ganglia of the venus clam on the basis of its cardiovascular activity [21]. Since then, a number of RFRPs have been characterized in both invertebrates [7], [16] and vertebrates [4], [6], and shown to exert a large array of biological activities [7]. For instance, neuropeptide FF (NPFF), the first mammalian RFRP that has been characterized [30], attenuates morphine-induced analgesia [13], [18], [30], inhibits food intake [8], [28], reduces locomotor activity [3], [22] increases arterial blood pressure [24], stimulates prolactin release [1] and inhibits aldosterone secretion [14].

A 26-amino acid peptide exhibiting the Arg–Phe–NH2 signature at its C-terminus has been recently isolated from a frog brain extract, and termed 26RFa [5]. This peptide does not show any appreciable sequence similarity with the other RFRPs identified so far, indicating that 26RFa is a brand-new member of this family [6]. The cDNA encoding the 26RFa precursor has been characterized in rat [5], [9], [11], mouse [9], [11], ox [9] and human [5], [9], [11], and it appears that the primary structure of 26RFa has been strongly preserved across vertebrates. The 26RFa precursor possesses several basic amino acids that may serve as cleavage-recognition signals for prohormone-convertases [27]. As shown in Fig. 1, processing at a single Arg located upstream of 26RFa may generate an N-terminally extended form of 43 amino acids (43RFa). Indeed, it has been shown that 43RFa is produced in CHO cells transfected with the pre-pro26RFa cDNA [9]. The existence of a tribasic endoproteolytic signal within the 26RFa sequence (Fig. 1) suggests that the peptide may be cleaved by prohormone-convertases to produce two fragments, i.e. 26RFa1–16 and 26RFa20–26. In addition, the human precursor encompasses another RFamide peptide of 9-amino acids (termed 9RFa) that is delimited by single Arg residues at its N- and C-terminal extremities (Fig. 1). The three-dimensional structure of 26RFa consists of a well-defined central amphipathic helix flanked by two N- and C-terminal disordered regions [29].

26RFa and 43RFa act as endogenous ligands of the G protein-coupled receptor GPR103 [9], [11]. The genes encoding the 26RFa precursor and GPR103 are both actively expressed in hypothalamic nuclei involved in the control of energy homeostasis [5], suggesting that 26RFa and/or 43RFa may regulate feeding behavior. In fact, intracerebroventricular (i.c.v.) administration of 26RFa in mice was found to stimulate food consumption in a dose-dependent manner [5].

Structure–activity relationship studies conducted on transfected cells have shown that both 26RFa and 43RFa are potent ligands of GPR103 while 9RFa has a very low affinity [9]. However, besides the orexigenic activity of 26RFa [5], nothing is known regarding the behavioral effects of pro26RFa-derived peptides. In the present study, we have investigated the effect of i.c.v. administration of 26RFa and various related peptides on food consumption and locomotor activity in mice.

Section snippets

Animals

Male Swiss albinos CD1 mice (IFFA-CREDO/Charles River, Saint-Germain sur l’Arbresle, France), weighting 22–25 g were housed 20 in Makrolon cages (L: 40 cm, W: 25 cm, H: 18 cm), with free access to standard semi-synthetic laboratory diet and tap water, under controlled temperature (22 ± 1 °C) and lighting (light on from 7:00 a.m. to 7:00 p.m.). Each animal was used once. Animal manipulations were performed according to the European Community Council Directive of 24 November 1986 (86/609/EEC), and were

Effects of 26RFa and related peptides on food consumption

In food-restricted mice, i.c.v. injection of 1 μg of 26RFa, 43RFa, 26RFa20–26 or 9RFa per mouse caused an increase in food intake which was statistically significant during the first and second period of testing. In contrast, at the same 1-μg dose, 26RFa1–16, 26RFa8–16 and NPFF had no effect on food intake (Fig. 2).

Effects of 26RFa and related peptides on locomotor activity

i.c.v. administration of graded doses (10, 100 or 1000 ng/mouse) of 26RFa, 43RFa or 26RFa1–16 elicited a dose-dependent increase in both horizontal (Fig. 3) and vertical (Fig. 4)

Discussion

In the rat brain, the gene encoding the novel neuropeptide 26RFa is almost exclusively expressed in the ventromedial hypothalamic nucleus and the lateral hypothalamic area [5], two hypothalamic nuclei that control appetite and energy homeostasis. Consistent with this observation, we have previously shown that 26RFa induces a dose-dependent stimulation of food intake in mice [5]. The human 26RFa precursor has the potential to generate several mature peptides including 26RFa, 43RFa, 26RFa20–26

Acknowledgments

This work was supported by CNRS (FRE 2735), INSERM (U 413), the Regional Platform for Cell Imaging, the European Institute for Peptide Research (IFRMP 23), and the Conseil Régional de Haute-Normandie.

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