title: Antibodies against the melanocortin-4 receptor act as inverse agonists in vitro and in vivo.
abstract: Functionally active antibodies (Abs) against central G-protein-coupled receptors have not yet been reported. We selected the hypothalamic melanocortin-4 receptor (MC4-R) as a target because of its crucial role in the regulation of energy homeostasis. A 15 amino acid sequence of the N-terminal (NT) domain was used as an antigen. This peptide showed functional activity in surface plasmon resonance experiments and in studies on HEK-293 cells overexpressing the human MC4-R (hMC4-R). Rats immunized against the NT peptide produced specific antibodies, which were purified and characterized in vitro. In HEK-293 cells, rat anti-NT Abs showed specific immunofluorescence labeling of hMC4-R. They reduced the production of cAMP under basal conditions and after stimulation with a synthetic MC4-R agonist. Rats immunized against the NT peptide developed a phenotype consistent with MC4-R blockade, that is, increased food intake and body weight, increased liver and fat pad weight, and elevated plasma triglycerides. In a separate experiment in rats, an increase in food intake could be produced after injection of purified Abs into the third ventricle. Similar results were obtained in rats injected with anti-NT Abs raised in rabbits. Our data show for the first time that active immunization of rats against the NT sequence of the MC4-R results in specific Abs, which appear to stimulate food intake by acting as inverse agonists in the hypothalamus.
authors.affiliation: Applied Pharmacology, Biozentrum, University of Basel, Basel, Switzerland.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Peter
authors.forename: Janet R
authors.initials: JR
authors.lastname: Nicholson
authors.forename: Déborah
authors.initials: D
authors.lastname: Heydet
authors.forename: Anne-Catherine
authors.initials: AC
authors.lastname: Lecourt
authors.forename: Johan
authors.initials: J
authors.lastname: Hoebeke
authors.forename: Karl G
authors.initials: KG
authors.lastname: Hofbauer
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology*; D001835:Body Weight / Q000276:immunology*; D002460:Cell Line; D004435:Eating / Q000276:immunology*; D005260:Female; D006801:Humans; D007031:Hypothalamus / Q000276:immunology*; D007668:Kidney / Q000276:immunology*; D008297:Male; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D044105:Receptor, Melanocortin, Type 4 / Q000276:immunology*
chemical_list: D000906:Antibodies; D044105:Receptor, Melanocortin, Type 4