Pharmacological function of melanocortin-3 receptor in goldfish (Carassius auratus).

The melanocortin-3 receptor (MC3R) was recognized for its critical role in energy metabolism and inflammatory responses in mammals; however, its functions in fish remain poorly understood. This study characterized the mc3r gene in goldfish, investigating its sequence, tissue distribution, and pharmacological responses. The coding sequence of goldfish mc3r was 975 bp, translating to a 325-amino-acid protein typical of G protein-coupled receptors, with notable conservation across cyprinids. Quantitative PCR analysis revealed high expression levels in the brain. Luciferase assays demonstrated that various agonists, particularly NDP-MSH and ACTH (1-24), effectively activated the cAMP and MAPK/ERK signaling pathways. Furthermore, all agonists tested (α-MSH, β-MSH, ACTH (1-24), and NDP-MSH) significantly inhibited NF-κB signaling, correlating with their activation of cAMP. These findings enhanced our understanding of the melanocortin system's role in regulating energy metabolism and inflammatory processes in teleost fish.