MC4R is a G protein-coupled receptor that binds melanocyte-stimulating hormones (α-MSH, β-MSH) and ACTH, products of the POMC precursor 12. It functions as a central component of the leptin-melanocortin pathway essential for energy homeostasis 3. Upon activation, MC4R couples to Gs proteins, stimulating adenylate cyclase and cAMP signaling to promote anorexogenic signaling in the hypothalamus and suppress appetite 42. The Agouti-related protein AGRP antagonizes this pathway, stimulating appetite 5. MC4R also modulates paraventricular nucleus neuron firing via KCNJ13 regulation 3 and interacts with OPN3 to inhibit cAMP signaling and promote food intake 6. Loss-of-function MC4R mutations cause severe early-onset obesity and are found in 1-5% of severely obese individuals 7, while gain-of-function variants protect against obesity, type 2 diabetes, and coronary artery disease through β-arrestin signaling bias 8. MC4R localization to neuronal primary cilia, mediated by MRAP2, is essential for weight regulation 9. The MC4R agonist Setmelanotide, FDA-approved for obesity from POMC/PCSK1/LEPR deficiency, demonstrates therapeutic potential 10. Notably, MC4R deficiency is associated with reduced cardiovascular disease risk despite obesity, indicating MC4R's role in lipid metabolism regulation 11.