Synergistic interaction between neuropeptide Y₁ and Y₅ receptor pathways in regulation of energy homeostasis

Abstract

Neuropeptide Y plays a key role in the physiological control of energy homeostasis. Five neuropeptide Y receptor subtypes have been cloned, and multiple neuropeptide Y receptor subtypes are thought to mediate neuropeptide Y activity. However, interactions among neuropeptide Y receptor subtypes have not been elucidated to date. Herein, we examined the interaction between neuropeptide Y₁ and Y₅ receptors in feeding regulation by employing selective neuropeptide Y₁ and Y₅ receptor antagonists in C57BL/6 and neuropeptide Y₁ receptor knockout mice fed a high-fat diet. A single-dose of a neuropeptide Y₁ receptor antagonist (10–30 mg/kg) suppressed spontaneous food intake and reduced body weight in high-fat diet-fed C57BL/6 mice, while treatment with a neuropeptide Y₅ receptor antagonist did not significantly reduce food intake or body weight. Coadministration of a neuropeptide Y₁ receptor antagonist with a neuropeptide Y₅ receptor antagonist further suppressed food intake and reduced body weight. Next, we evaluated the chronic efficacy of a neuropeptide Y₅ receptor antagonist in high-fat diet-fed neuropeptide Y₁ receptor knockout mice in order to mimic chronic combination treatment with neuropeptide Y₁ and Y₅ receptor antagonists. The neuropeptide Y₅ receptor antagonist produced greater body weight reductions in high-fat diet-fed neuropeptide Y₁ receptor knockout mice than in wild-type C57BL/6 mice. These findings confirm an interaction between neuropeptide Y₁ and Y₅ receptors in the regulation of energy homeostasis, as blockade of both the neuropeptide Y₁ and Y₅ receptors produced a greater anti-obesity effect than blocking either receptor alone.

Introduction

Several lines of evidence have shown that the hypothalamus plays a key role in energy homeostasis and that a number of hypothalamic neuropeptides are involved in energy balance. Neuropeptide Y, a 36-amino acid peptide neurotransmitter, is one of the most potent orexigenic peptides identified to date. The physiological functions of neuropeptide Y are mediated by activation of G-protein-coupled receptors. Five types of neuropeptide Y receptors, Y₁, Y₂, Y₄, Y₅ and mY₆, have been cloned, with Y₁, Y₂ and Y₅ receptors being abundantly expressed in the hypothalamus (Parker et al., 2002) and playing a role in feeding regulation. Neuropeptide Y₁ and Y₅ receptor selective agonists stimulate feeding (Gerald et al., 1996, Mullins et al., 2001), while neuropeptide Y₂ receptor selective agonists inhibit feeding (Batterham et al., 2002). Thus, neuropeptide Y₁ and Y₅ receptors mediate orexigenic effects, while neuropeptide Y₂ receptors mediate anorexigenic effects.

We previously reported that neuropeptide Y-induced food intake was reduced in neuropeptide Y₁ receptor knockout mice, but not in neuropeptide Y₅ receptor knockout mice, indicating that the neuropeptide Y₁ receptor plays a major role in neuropeptide Y-induced feeding (Kanatani et al., 2000b). Interestingly, despite the limited efficacy of the neuropeptide Y₅ receptor-preferring agonists at the neuropeptide Y₁ receptor, human pancreatic polypeptide-induced food intake was significantly diminished in neuropeptide Y₁ receptor knockout mice (Kanatani et al., 2000b). This indicates that the neuropeptide Y₁ receptor modulates the action of the neuropeptide Y₅ receptor. In addition, both neuropeptide Y₁ and Y₅ receptor knockout mice paradoxically develop late-onset obesity (Pedrazzini et al., 1998, Marsh et al., 1998). Compensatory changes of the remaining neuropeptide Y receptors, such as neuropeptide Y₅ or Y₁ receptor, may occur in neuropeptide Y₁ and Y₅ receptor knockout mice, and these changes may contribute to the obese phenotypes of these knockout mice. We thus hypothesized that there are interactions among neuropeptide Y receptor subtypes, particularly neuropeptide Y₁ and Y₅ receptors.

In the present study, we conducted experiments in order to clarify the interactions between neuropeptide Y₁ and Y₅ receptors in feeding regulation by using selective neuropeptide Y₁ (Kanatani et al., 2001) and Y₅ receptor antagonists (Mashiko et al., 2008). We previously reported that a neuropeptide Y₁ receptor antagonist suppressed spontaneous food intake in db/db and C57BL/6 mice (Kanatani et al., 2001), while a neuropeptide Y₅ receptor antagonist specifically produced anti-obesity effects in high-fat diet-fed obesity animals (Ishihara et al., 2006, Mashiko et al., 2008). Therefore, we initially examined the acute anorexigenic effects of combined treatment of neuropeptide Y₁ and Y₅ receptor antagonists in high-fat diet-fed obese C57BL/6 mice. Next, we examined the chronic effects of neuropeptide Y₅ receptor antagonist in high-fat diet-fed obese neuropeptide Y₁ receptor knockout mice in order to mimic chronic exposure to combined treatment with neuropeptide Y₁ and Y₅ receptor antagonists.