Receptor · Melanocortin 3 receptor
MC3R — the energy-partitioning receptor
MC4R's quieter sibling in the hypothalamus. Rather than switching appetite on and off, MC3R governs how the body spends its energy — and, it turns out, the timing of growth and puberty.
- Tissue
- Hypothalamus; gut, heart, immune cells
- Ligands
- α-, β-, γ-MSH, ACTH; AgRP (antagonist)
- Function
- Tunes energy partitioning, the timing of puberty and growth, and natriuresis; a brake complementing MC4R.
- When it fails
- Disruption shifts fat mass and feeding rhythm; a key modulator of the linear-growth/puberty axis.
MC3R shares the hypothalamus with MC4R and responds to the same melanocortin peptides, yet it does a different job. For years it was the harder of the two central receptors to pin down — clearly involved in energy balance, but not in the simple "eat / don't eat" way of MC4R.[1] Recent human genetics has given it a much sharper identity.
Energy partitioning, not just intake
Like the rest of the family, MC3R couples to Gs and cyclic AMP, and γ-MSH is a relatively potent agonist at this subtype while AgRP antagonises it.[3]But the phenotype of losing MC3R is distinctive: animal models point less to raw appetite and more to how energy is partitioned — the balance of fat versus lean mass and the efficiency with which food is used. MC3R also acts within the hypothalamic circuitry itself, modulating the POMC and AgRP neurons that feed into MC4R.[1]
The growth-and-puberty switch
The clearest picture of MC3R's purpose came in 2021. People carrying loss-of-function MC3R variants — including a rare individual with two defective copies — were found to have later puberty, reduced linear growth, lower lean mass, and lower circulating IGF-1; mice lacking Mc3r showed delayed sexual maturation and a reproductive cycle that no longer responded normally to nutritional state.[2] The interpretation is elegant: the same nutrient-sensing melanocortin system bifurcates — signalling through MC4R to control how much energy is acquired, and through MC3R to decide how that energy is spent on growing up.[2]
Inflammation and the periphery
MC3R is not confined to the brain. It is expressed in the gut, heart, kidney, placenta, and on immune cells, where melanocortin signalling through MC3R is broadly anti-inflammatory and pro-resolving — part of why the receptor is studied as a target in inflammatory disease.[1] For how MC3R sits alongside the other four receptors, see theoverview pillar; for the appetite arm it complements, seeMC4R.
References
- 1.Cone RD. Studies on the physiological functions of the melanocortin system. Endocr Rev. 27(7):736–49. 2006. link ↗
- 2.Lam BYH, Williamson A, Finer S, et al. MC3R links nutritional state to childhood growth and the timing of puberty. Nature. 599(7885):436–41. 2021. link ↗
- 3.Cooray SN, Clark AJL. The melanocortin receptors and their accessory proteins. Front Endocrinol (Lausanne). 4:9. 2013. link ↗