title: Ligand-directed trafficking of the δ-opioid receptor in vivo: two paths toward analgesic tolerance.
abstract: δ-Opioid receptors are G-protein-coupled receptors that regulate nociceptive and emotional responses. It has been well established that distinct agonists acting at the same G-protein-coupled receptor can engage different signaling or regulatory responses. This concept, known as biased agonism, has important biological and therapeutic implications. Ligand-biased responses are well described in cellular models, however, demonstrating the physiological relevance of biased agonism in vivo remains a major challenge. The aim of this study was to investigate the long-term consequences of ligand-biased trafficking of the δ-opioid receptor, at both the cellular and behavioral level. We used δ agonists with similar binding and analgesic properties, but high [SNC80 ((+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide)]- or low [ARM390 (N,N-diethyl-4-(phenyl-piperidin-4-ylidenemethyl)-benzamide)]-internalization potencies. As we found previously, a single SNC80-but not ARM390-administration triggered acute desensitization of the analgesic response in mice. However, daily injections of either compound over 5 d produced full analgesic tolerance. SNC80-tolerant animals showed widespread receptor downregulation, and tolerance to analgesic, locomotor and anxiolytic effects of the agonist. Hence, internalization-dependent tolerance developed, as a result of generalized receptor degradation. In contrast, ARM390-tolerant mice showed intact receptor expression, but δ-opioid receptor coupling to Ca²+ channels was abolished in dorsal root ganglia. Concomitantly, tolerance developed for agonist-induced analgesia, but not locomotor or anxiolytic responses. Therefore, internalization-independent tolerance was produced by anatomically restricted adaptations leading to pain-specific tolerance. Hence, ligand-directed receptor trafficking of the δ-opioid receptor engages distinct adaptive responses, and this study reveals a novel aspect of biased agonism in vivo.
authors.affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique/Institut National de la Santé et de la Recherche Médicale/Université de Strasbourg, 67404 Illkirch, France. amynahpradhan@ucla.edu
authors.forename: Amynah A A
authors.initials: AA
authors.lastname: Pradhan
authors.forename: Wendy
authors.initials: W
authors.lastname: Walwyn
authors.forename: Chihiro
authors.initials: C
authors.lastname: Nozaki
authors.forename: Dominique
authors.initials: D
authors.lastname: Filliol
authors.forename: Eric
authors.initials: E
authors.lastname: Erbs
authors.forename: Audrey
authors.initials: A
authors.lastname: Matifas
authors.forename: Christopher
authors.initials: C
authors.lastname: Evans
authors.forename: Brigitte L
authors.initials: BL
authors.lastname: Kieffer
mesh_terms: D000700:Analgesics / Q000494:pharmacology* / Q000627:therapeutic use; D000818:Animals; D001549:Benzamides / Q000494:pharmacology / Q000627:therapeutic use; D001921:Brain / Q000648:ultrastructure; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000235:genetics; D004195:Disease Models, Animal; D004347:Drug Interactions; D004361:Drug Tolerance / Q000235:genetics / Q000502:physiology*; D005260:Female; D005620:Freund's Adjuvant; D005727:Ganglia, Spinal / Q000166:cytology; D049452:Green Fluorescent Proteins / Q000235:genetics; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006930:Hyperalgesia / Q000188:drug therapy / Q000503:physiopathology; D007249:Inflammation / Q000139:chemically induced / Q000150:complications; D008024:Ligands; D008124:Locomotion / Q000187:drug effects / Q000235:genetics; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010146:Pain / Q000188:drug therapy / Q000209:etiology; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods; D010879:Piperazines / Q000494:pharmacology / Q000627:therapeutic use; D010880:Piperidines / Q000494:pharmacology / Q000627:therapeutic use; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000235:genetics / Q000502:physiology; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D011984:Sensory Receptor Cells / Q000187:drug effects; D013116:Spinal Cord / Q000648:ultrastructure; D018709:Statistics, Nonparametric; D013460:Sulfur Isotopes / Q000378:metabolism; D013997:Time Factors
chemical_list: D000700:Analgesics; D001549:Benzamides; D008024:Ligands; C415566:N,N-diethyl-4-(phenylpiperidin-4-ylidenemethyl)benzamide; D010879:Piperazines; D010880:Piperidines; D017465:Receptors, Opioid, delta; D013460:Sulfur Isotopes; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; C088464:4-(alpha-(4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl)-N,N-diethylbenzamide; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D005620:Freund's Adjuvant; D002118:Calcium