Functional Characterization and Pharmacological Rescue of Nine Novel Naturally Occurring Human Melanocortin-4 Receptor Mutations

Presentation Number: SUN 247
Date of Presentation: April 2nd, 2017

Wei Wang*1, Meng-Hong Dai2, Xiu-Lei Mo2 and Ya-Xiong Tao1
1Auburn University, Auburn, AL, 2Auburn University

Abstract

The melanocortin-4 receptor (MC4R) is a member of family A G protein-coupled receptors. Extensive studies suggest that MC4R is critically involved in regulating food intake and energy expenditure. Mutations in the MC4R have been identified as the most common monogenic form of human obesity. To support a causal role of MC4R mutations in obesity pathogenesis, we performed systematic functional characterization of nine novel human MC4R mutations (including L23R, K73R, T101N, T112K, M161T, L207V, M215L, R310K, and I316S) that have not been studied in detail before. We showed that eight mutants had normal total expression and five mutants had decreased cell surface expression compared with wild-type hMC4R. Using NDP-MSH or a-MSH as the ligand, we further showed that four mutants were defective in ligand binding and three mutants were impaired in downstream cAMP generation. We also measured the signaling properties of all the mutants in the ERK1/2 signaling pathway since activation of ERK1/2 cascade has been suggested to be related to MC4R regulation of energy homeostasis in vivo. Five mutants with normal agonist-dependent cAMP generation were defective in the agonist-stimulated ERK1/2 signaling, suggesting that these mutant MC4Rs were biased receptors and defective ERK1/2 signaling might be a cause of obesity in patients harboring Class V mutant MC4Rs. Furthermore, we demonstrated that two MC4R inverse agonists, Ipsen 5i and ML00253764, acted as pharmacological chaperones to rescue the cell surface expression and function of two severely intracellularly retained mutant MC4Rs. In summary, we provided detailed functional data and a potential therapeutic approach for the treatment of obese patients harboring these MC4R mutations.

 

Nothing to Disclose: WW, MHD, XLM, YXT