Pharmacological Characterization of Canine Melanocortin-4 Receptor and Its Natural Variant V213F

Abstract

Obesity is becoming one of the most significant public health problems all over the world, especially in some developed countries. During the past decade, genetic factors associated with obesity have gained more attention. Rodent and human genetic studies showed that leptin-regulated melanocortin circuit plays an important role in regulating food intake and body weight. As one of the components in the circuit, melanocortin-4 receptor (MC4R) was shown to play a critical role in regulation of food intake and energy expenditure. Mutations in MC4R were identified to be the most common monogenic form of obesity in humans. Recently, studies on role of MC4R in regulation of food intake have been extended to other mammalian species, such as pigs. In the current study, the newly identified canine MC4R (cMC4R) natural variantV213F was generated by site-directed mutagenesis using WT cMC4R as the template. Both WT receptor and the natural variant were expressed in HEK293T cells. Pharmacological characteristics of these receptors were analyzed by binding and signaling assays upon the stimulation of three agonists: [Nle4, D-Phe7]-α-melanocyte stimulating hormone (NDP-MSH), α-MSH, and β-MSH. WT human MC4R (hMC4R) was included in the experiments for comparison. NDP-MSH was shown to be the most potent agonist for cMC4R and therefore would be better suited for further in vivo studies. Both WT cMC4R and its natural variant functioned normally in terms of binding and signaling, similar to WT hMC4R. In conclusion, our results showed that cMC4R functioned normally upon stimulation with three MC4R agonists. Its natural variant V213F does not have any functional defect and therefore is not likely to cause obesity in dogs. NDP-MSH would be a better ligand for the further in vivo studies. Further studies may focus on whether cMC4R respond to analog that has been tested in human medicine similarly as hMC4R.