Evolution and Pharmacology of Receptors for Bradykinin and Neuropeptide Y in Vertebrates

The bradykinin and neuropeptide Y (NPY) receptors belong to the superfamily of G-protein coupled receptors (GPCRs). The GPCRs form the largest class of therapeutic targets and it is therefore of great interest to investigate the pharmacological properties, functions and evolution of these receptors. Bradykinin (BK) is a nonapeptide that contributes to inflammatory responses, mediates pain signals and influences blood pressure. The two bradykinin receptor subtypes B1 and B2 are well characterized in mammals, but have received little attention in non-mammals. This thesis describes the cloning and characterization of the first piscine bradykinin receptor, from the Danio rerio (zebrafish). Ligand-receptor interactions were measured as production of intracellular inositol phosphate. Zebrafish BK activated the receptor with highest potency (pEC50=6.97±0.1) while mammalian BK was almost inactive. A complete alanine and D-amino acid scan of the BK peptide revealed important roles for receptor interaction for residues Gly4, Ser6, Pro7, Leu8 and Arg9. The receptor gene was mapped to chromosome 17 in the zebrafish genome in a region that shows conserved synteny to the human B1-B2 gene region on chromosome 14. The release of the zebrafish and pufferfish genomes enabled us to identify both B1 and B2 genes in Danio rerio and pufferfishes (Takifugu rubripes and Tetraodon nigroviridis) as well as the B1 gene in chicken. All of these species display conserved synteny of the gene region. Interestingly, the evolutionary rate is clearly greater for B1 than for B2. Kininogen, the precursor for bradykinin, is also located in a chromosome region with extensive conserved synteny. Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) comprise a family of related peptides and are involved in a variety of neuronal and endocrine functions. Receptor subtypes Y6 and Y7 were cloned and pharmacologically characterized in chicken. The genes are located one megabase apart on chromosome 13 in a region with conserved synteny to human chromosome 5. Porcine PYY bound to chicken Y6 with a Kd of 0.80±0.36 nM and chicken Y7 with a Kd of 0.14±0.01 nM. The Y6 mRNA is expressed in hypothalamus, gastrointestinal tract and adipose tissue and may be involved in appetite regulation like other NPY receptors. Chicken Y7 mRNA was only detected in adrenal gland. These results may help explain why these receptors have lost function in humans