The apelin receptor (APJ) is a member of the G-protein coupled receptor gene family, encoded by the APLNR gene. The apelin receptor and its endogenous ligand, apelin, have been suggested to act as key mediators of physiological responses to multiple homeostatic actions, including cardiovascular control, water balance, hypothalamic–pituitary–adrenal (HPA) axis regulation and metabolic homeostasis.

Apelin receptor structure contains seven hydrophobic transmembrane domains, with several sites for phosphorylation by protein kinase A, and sites for palmitoylation and glycosylation. The N-terminal glycosylation is implicated in the receptor’s expression, stability, correct folding of the protein and ligand binding. The C-terminal palmitoylation has been reported to play a role in membrane association. These modifications can influence the internalization, dimerization and ligand binding of the receptor. Human apelin receptor shares 92% homology with mouse receptor and 90% homology with rat receptor.

Apelin expression can be detected in several brain regions including the human caudate nucleus, corpus callosum, hippocampus, substantia nigra, subthalamic nucleus, medulla and spinal cord. Apelin receptor is also expressed in the spleen, placenta and cardiovascular tissues and small amounts in the small intestine, lung, stomach, colonic mucosa and ovary.