RESUMO
The melanocortin-4 receptor (MC4R) is critically involved in regulating energy balance, and obesity has been observed in mice with mutations in the gene for brain-derived neurotrophic factor (BDNF). Here we report that BDNF is expressed at high levels in the ventromedial hypothalamus (VMH) where its expression is regulated by nutritional state and by MC4R signaling. In addition, similar to MC4R mutants, mouse mutants that expresses the BDNF receptor TrkB at a quarter of the normal amount showed hyperphagia and excessive weight gain on higher-fat diets. Furthermore, BDNF infusion into the brain suppressed the hyperphagia and excessive weight gain observed on higher-fat diets in mice with deficient MC4R signaling. These results show that MC4R signaling controls BDNF expression in the VMH and support the hypothesis that BDNF is an important effector through which MC4R signaling controls energy balance.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/fisiologia , Metabolismo Energético/fisiologia , Hipotálamo Médio/metabolismo , Receptor Tipo 4 de Melanocortina/metabolismo , Receptores da Corticotropina/fisiologia , alfa-MSH/análogos & derivados , Animais , Peso Corporal , Fator Neurotrófico Derivado do Encéfalo/genética , Ritmo Circadiano/fisiologia , Comportamento Alimentar , Feminino , Masculino , Melaninas/genética , Melaninas/metabolismo , Camundongos , Receptores da Corticotropina/genética , alfa-MSH/administração & dosagemRESUMO
The central melanocortin system has been demonstrated to play an important role in regulating different aspects of energy homeostasis. Understanding the specific contributions of MC3 and MC4 receptors, however, requires specific agonists and antagonists for each of the predominant forms of brain melanocortin receptors, MC3-R and MC4-R. We report here the characterization of a small peptide mimetic MC4-R-specific agonist that possesses both high affinity (K(i)=11.3 nM) and potency (EC(50)=1.62 nM) in vitro and is capable of inhibiting feeding behavior in mice when administered intracerebroventricularly (i.c.v.). Depending on the paradigm, acute (1 h following an overnight fast) or long-term (greater than 6 h under normal nocturnal feeding conditions) feeding inhibition was observed following icv injection. No effect on long-term feeding inhibition was observed with this compound in MC4-R knockout mice, and central administration of this compound had no effect on either metabolic rate or insulin release.