Pharmacological and immunohistochemical characterization of the APJ receptor and its endogenous ligand apelin

J Neurochem. 2003 Mar;84(5):1162-72. doi: 10.1046/j.1471-4159.2003.01587.x.


Apelin peptides have recently been identified to be the endogenous ligands for the G protein-coupled receptor APJ. However, little is known about the physiological roles of this ligand-receptor pairing. In the present study we investigated the pharmacology of several apelin analogues at the human recombinant APJ receptor using radioligand binding and functional assays. This has led to the identification of key residues in the apelin peptide required for functional potency and binding affinity through structure-activity studies. In particular, we have identified that replacement of leucine in position 5, or arginine in position 2 and 4 of the C-terminal apelin peptide, apelin-13, resulted in significant changes in pharmacology. We also investigated the detailed localization of pre-proapelin and APJ receptor mRNA in a wide range of human, rat and mouse tissues using quantitative RT-PCR, and carried out a detailed immunohistochemical study of the distribution of the APJ receptor in rat brain and spinal cord. Interestingly, the APJ receptor was not only co-localized in white matter with GFAP in the spinal cord, but was also clearly localized on neurones in the brain, suggesting that this receptor and its peptide may be involved in a wide range of biological process yet to be determined.

MeSH terms

  • Adipokines
  • Amino Acid Substitution
  • Animals
  • Apelin
  • Apelin Receptors
  • Binding, Competitive / physiology
  • Blotting, Western
  • Brain / metabolism
  • Carrier Proteins / biosynthesis
  • Carrier Proteins / chemistry*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cell Line
  • Cyclic AMP / metabolism
  • Fluorometry
  • Humans
  • Immunohistochemistry
  • Intercellular Signaling Peptides and Proteins
  • Ligands
  • Mice
  • Mutagenesis, Site-Directed
  • Organ Specificity
  • Protein Binding / physiology
  • Radioligand Assay
  • Rats
  • Receptors, Dopamine D2 / chemistry*
  • Receptors, Dopamine D2 / genetics
  • Receptors, Dopamine D2 / metabolism*
  • Receptors, G-Protein-Coupled*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Spinal Cord / metabolism
  • Structure-Activity Relationship


  • APLN protein, human
  • APLNR protein, human
  • Adipokines
  • Apelin
  • Apelin Receptors
  • Apln protein, mouse
  • Apln protein, rat
  • Aplnr protein, mouse
  • Aplnr protein, rat
  • Carrier Proteins
  • Intercellular Signaling Peptides and Proteins
  • Ligands
  • Receptors, Dopamine D2
  • Receptors, G-Protein-Coupled
  • Cyclic AMP