MON-672 Role Of Ligand- And Genetic Variant Dependent Melanocortin 4 Receptor (mc4r) Bias Signaling For The Individual Risk To Develop Obesity

Abstract Disclosure: L. Ruck: None. P. Scheerer: None. S. Paisdzior: None. S. Wiegand: None. G. Kleinau: None. N. Heyder: None. P. Gmach: None. S. Jyrch: None. A. Beck-Sickinger: None. M. Troll: None. H. Biebermann: None. P. Kühnen: None. Introduction: The melanocortin 4 receptor (MC4R), a G protein-coupled receptor (GPCR), is a critical regulator of body weight within the hypothalamus and is embedded in the leptin-melanocortin signaling pathway. Heterozygous MC4R gene mutations have been identified as potent genetic risk factors for the development of obesity. Additionally, the MC4R agonist setmelanotide has recently been approved as a pharmacological treatment option for patients with certain rare monogenic forms of obesity. In recent years it has been described that MC4R related differential (biased) signaling is playing an important role for body weight regulation and the downstream effect of MC4R ligands. However, the interplay between MC4R genetic variants and different endogenous and external MC4R ligands remains elusive. Methods: We analyzed in vitro the signaling of 20 heterozygous MC4R mutations, which have been identified in a cohort of children with obesity, in regards to Gs, Gq/11, ERK, G12/13 and b-arrestin2 recruitment and after stimulation with different MC4R ligands (α-MSH, β-MSH, setmelanotide) in HEK293 cells. Additionally, MC4R mutations were further characterized by analysis of our previously solved the cryo-electron microscopic (cyro-EM) structures. Results: We observed a ligand and genetic variant dependent differential (bias) signaling of the MC4R. The “protective” MC4R variant V103I was associated with an increase of Gq signaling after stimulation with α-MSH. Contrary to the complete loss of function variants like Y80C, D90N and S127L (deficit in all analyzed pathways), MC4R variants as S77L or T178M led to a reduction of non-Gs signaling cascades while Gs signaling was not altered. These signaling profiles were ligand dependent, which was partially related to MC4R conformation changes, which were analyzed based on cryo-EM structure data. Conclusion: Our findings emphasize the critical role of differential (bias) signaling for MC4R function. Cryo-EMStructural data- combined with in vitro functional data allowed to gain further insights into the structural regulation of the MC4R, which can be relevant to optimized MC4R agonists as a treatment option for patients with certain forms of obesity. Presentation: Monday, July 14, 2025