Roger D. Cone

Most antipsychotic drugs (APDs) cause hyperphagia and weight gain, yet the neural mechanisms underlying these metabolic side effects remain elusive, in part due to difficulties in modeling them in rodents. Here, we establish a mouse model that recapitulates clozapine-induced metabolic syndrome, enabling mechanistic investigation of this widely prescribed APD. We show that clozapine promotes obesity in female mice by driving hyperphagia, which requires functional coupling between the melanocortin 4 receptor (MC4R) and the Kir7.1 potassium channel. Within the broader context of clozapine’s polypharmacology, this signaling axis emerges as a critical downstream convergence node for APD-induced metabolic dysfunction. Mechanistically, clozapine inhibits MC4R-expressing neurons in the paraventricular nucleus of the hypothalamus by enhancing MC4R-Kir7.1 coupling, thereby increasing inward potassium currents. Notably, clozapine produces this inhibition without binding the MC4R orthosteric site and without engaging canonical Gαs signaling. Genetic deletion of Kir7.1 in MC4R neurons or pharmacological inhibition of Kir7.1 reverses clozapine-induced weight gain while preserving its behavioral efficacy in established antipsychotic assays. Together, these findings reveal a G-protein-independent mechanism by which clozapine disrupts energy balance and identify MC4R-Kir7.1 coupling as a therapeutically tractable pathway for mitigating APD-associated metabolic dysfunction.

The melanocortin 4 receptor (MC4R) plays a critical role in the central control of energy homeostasis and its disruption causes severe early onset obesity. The MC4R agonist Imcivree has been approved for the treatment of certain genetic obesity syndromes. Here we demonstrate that the membrane-spanning protein Attractin-like protein 1 (ATRNL1) directly interacts with MC4R to amplify its signaling in cells and that expression of ATRNL1 potentiates the activation of MC4R neurons by MC4R agonists in mice. Disruption of ATRNL1 in the PVN of the hypothalamus causes increased food intake and obesity, which cannot be rescued by MC4R agonist treatment. In exomes from 927 children with severe early-onset obesity, we identified 21 rare ATRNL1 variants. Eleven of 17 variants studied in cells impaired ATRNL1-mediated regulation of MC4R signaling, including variants ultra-rare or absent from UK Biobank and other populations. Cumulatively, these findings establish ATRNL1 as an important regulator of mammalian energy homeostasis.

Reducing macrocycle size while preserving the melanocortin pharmacophore provides a means to tune functional activity and receptor preference at h MC3R and h MC4R.

The melanocortin-3 receptor (MC3R) regulates GABA release from agouti-related protein (AgRP) nerve terminals and thus tonically suppresses multiple circuits involved in feeding behavior and energy homeostasis. Here, we examined the role of the MC3R and the melanocortin system in regulating the response to various anorexigenic agents. The genetic deletion or pharmacological inhibition of the MC3R, or subthreshold doses of an MC4R agonist, improved the dose responsiveness to glucagon-like peptide 1 (GLP1) agonists, as assayed by inhibition of food intake and weight loss. An enhanced anorectic response to the acute satiety factors peptide YY (PYY3-36) and cholecystokinin (CCK) and the long-term adipostatic factor leptin demonstrated that increased sensitivity to anorectic agents was a generalized result of MC3R antagonism. We observed enhanced neuronal activation in multiple hypothalamic nuclei using Fos IHC following low-dose liraglutide in MC3R-KO mice ( Mc3r ^–/– ), supporting the hypothesis that the MC3R is a negative regulator of circuits that control multiple aspects of feeding behavior. The enhanced anorectic response in Mc3r ^–/– mice after administration of GLP1 analogs was also independent of the incretin effects and malaise induced by GLP1 receptor (GLP1R) analogs, suggesting that MC3R antagonists or MC4R agonists may have value in enhancing the dose-response range of obesity therapeutics.

SUMMARY: Most antipsychotic drugs (APDs) induce hyperphagia and weight gain. However, the neural mechanisms are poorly understood, partly due to challenges replicating their metabolic effects in rodents. Here, we report a new mouse model that recapitulates overeating induced by clozapine, a widely prescribed APD. Our study shows that clozapine boosts food intake by inhibiting melanocortin 4 receptor (MC4R) expressing neurons in the paraventricular nucleus of the hypothalamus. Interestingly, neither clozapine nor risperidone, another commonly used APD, affects receptor-ligand binding or the canonical Gαs signaling of MC4R. Instead, they inhibit neuronal activity by enhancing the coupling between MC4R and Kir7.1, leading to the open state of the inwardly rectifying potassium channel. Deletion of Kir7.1 in Mc4r-Cre neurons prevents clozapine-induced weight gain, while treatment with a selective Kir7.1 blocker mitigates overeating in clozapine-fed mice. Our findings unveil a molecular pathway underlying the effect of APDs on feeding behavior and suggest its potential as a therapeutic target.

Hereditary defects in the function of the Kir7.1 in the retinal pigment epithelium are associated with the ocular diseases retinitis pigmentosa, Leber congenital amaurosis, and snowflake vitreal degeneration. Studies also suggest that Kir7.1 may be regulated by a GPCR, the melanocortin-4 receptor, in certain hypothalamic neurons. We present the first structures of human Kir7.1 and describe the conformational bias displayed by two pathogenic mutations, R162Q and E276A, to provide an explanation for the basis of disease and illuminate the gating pathway. We also demonstrate the structural basis for the blockade of the channel by a small molecule ML418 and demonstrate that channel blockade in vivo activates MC4R neurons in the paraventricular nucleus of the hypothalamus (PVH), inhibiting food intake and inducing weight loss. Preliminary purification, and structural and pharmacological characterization of an in tandem construct of MC4R and Kir7.1 suggests that the fusion protein forms a homotetrameric channel that retains regulation by liganded MC4R molecules.

Melanocortin 4 receptor (MC4-R) antagonists are actively sought for treating cancer cachexia. We determined the structures of complexes with PG-934 and SBL-MC-31. These peptides differ from SHU9119 by substituting His⁶ with Pro⁶ and inserting Gly¹⁰ or Arg¹⁰. The structures revealed two subpockets at the TM7-TM1-TM2 domains, separated by N285^7.36. Two peptide series based on the complexed peptides led to an antagonist activity and selectivity SAR study. Most ligands retained the SHU9119 potency, but several SBL-MC-31-derived peptides significantly enhanced MC4-R selectivity over MC1-R by 60- to 132-fold. We also investigated MC4-R coupling to the K⁺ channel, Kir7.1. Some peptides activated the channel, whereas others induced channel closure independently of G protein coupling. In cell culture studies, channel activation correlated with increased feeding, while a peptide with Kir7.1 inhibitory activity reduced eating. These results highlight the potential for targeting the MC4-R:Kir7.1 complex for treating positive and restrictive eating disorders.

The melanocortin-3 receptor (MC3R) acts presynaptically to regulate GABA release from agouti-related protein (AgRP) nerve terminals and thus may be a negative regulator of multiple circuits involved in feeding behavior and energy homeostasis. Here, we examined the role of MC3R in regulating the response to various anorexigenic agents. Our findings reveal that genetic deletion or pharmacological inhibition of MC3R improves the dose responsiveness to Glucagon-like peptide 1 (GLP1) agonists, as assayed by inhibition of food intake and weight loss. An enhanced anorectic response to other agents, including the acute satiety factors peptide YY (PYY _3-36 ) and cholecystokinin (CCK) and the long-term adipostatic factor, leptin, demonstrated that increased sensitivity to anorectic agents is a generalized result of MC3R antagonism. Enhanced neuronal activation in multiple nuclei, including ARH, VMH, and DMH, was observed using Fos immunohistochemistry following low-dose liraglutide in MC3R knockout mice ( Mc3r ^-/- ), supporting the hypothesis that the MC3R is a negative regulator of circuits regulating multiple aspects of feeding behavior. The enhanced anorectic response in Mc3r ^-/- mice after administration of GLP1 analogs was also independent of the incretin effects and malaise induced by GLP1R analogs, suggesting that MC3R antagonists may have value in enhancing the dose-response range of obesity therapeutics.