melanocortins

Melanocortins are a family of peptide hormones derived from proopiomelanocortin (POMC). The principal members are adrenocorticotropic hormone (ACTH) and the melanocyte-stimulating hormones α-MSH, β-MSH, and γ-MSH. These peptides arise from POMC through post-translational processing by prohormone convertases and are produced in the anterior pituitary and intermediate lobe corticotrophs and melanotrophs, as well as in various brain and peripheral tissues.

Melanocortins signal through a set of G protein-coupled receptors known as melanocortin receptors (MC1R–MC5R). Each receptor has distinct tissue distribution and functions: MC1R is important for pigmentation in melanocytes; MC2R is the ACTH receptor in the adrenal cortex, stimulating glucocorticoid synthesis; MC3R and MC4R are highly expressed in the brain and regulate energy homeostasis, feeding behavior, and autonomic functions; MC5R is found in exocrine glands and other tissues with diverse roles.

Physiological roles of melanocortins include stimulation of adrenal glucocorticoid production, modulation of inflammatory and immune responses, involvement in skin and hair pigmentation, and contributions to energy balance and appetite regulation. The anti-inflammatory properties of melanocortins are mediated through several receptor subtypes and downstream signaling pathways.

Clinical notes: genetic or functional alterations in the melanocortin system have disease associations. MC4R mutations are a common cause of obesity due to altered appetite and energy expenditure. MC1R variants influence pigmentation and, in some contexts, cancer risk. ACTH-related dysfunction can affect adrenal steroidogenesis.

In research, melanocortins are studied for their roles in inflammation, metabolism, and potential therapeutic applications targeting MC receptors.