Pharmacological Studies of Four Neuropeptide Y-family Receptor Subtypes

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: The neuropeptide Y (NPY) family of structurally related peptides includes NPY, peptide YY (PYY) and pancreatic polypeptide (PP). They bind to G-protein coupled receptors named Y receptors, and include in mammals Y1, Y2, Y4, Y5, Y6 and in non-mammalian vertebrates also Y7, Yb and Yc. Subtypes Y1 and Y5 stimulate appetite, while Y2 and Y4 have the opposite effect in mammals. The studies described here concern human Y1 and Y4, chicken Y6 and Y7, and zebrafish Y2. Site-directed mutagenesis of human Y1 identified sites important for binding of NPY and PYY as well as Y1 antagonists. The results clarify contradictory findings previously reported by others and identify new sites of interaction. A three-dimensional structural model of the Y1 receptor based upon the high-resolution structure of bovine rhodopsin was generated that increases our understanding of ligand-receptor interactions and hopefully will facilitate the design of novel subtype-selective agonists and antagonists. Two naturally occurring variants of human Y4 with substitutions R240C and V276M have been found in a sample of obese children. Functional studies in vitro showed that the cellular response to PP was greatly decreased for R240C and may provide a causative link to juvenile obesity. The genes for chicken Y6 and Y7 were found to be located ~1 megabase apart on chromosome 13 syntenic to the human Y6 pseudogene. Y6 mRNA has widespread expression whereas Y7 mRNA was found only in adrenal gland. Truncated fragments of PYY had lower affinity to chicken Y7 and zebrafish Y2 than to Y2 from mammals and chicken. The results suggest that Y2 in mammals acquired the ability to bind truncated PYY, i. e. PYY3-36, fairly recently, which has implications for its role in appetite inhibition.These differences between receptor subtypes in sequences and pharmacological properties will be useful to further elucidate the structure and activation of Y receptors by site-directed mutagenesis.