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The physiological relevance of functional selectivity in dopamine signalling.

ABSTRACT: We sought to determine the role of functionally selective dopamine (DA) signalling pathways (G protein or β-arrestin) in DA-dependent behaviours. Mice that were globally deficient for β-arrestins or mice deficient in GSK3β in D2 receptor (D2R)-expressing neurons were used to investigate the role of functional selectivity in DA-dependent behaviours such as locomotor activity and conditioned place preference (CPP). Wild-type or knockout mice were injected with drugs such as morphine and amphetamine, which are known to increase DA levels in the brain and to induce a hyper-locomotor response and CPP. Unlike β-arrestin1 (βarr1)-deficient mice, mice globally deficient for β-arrestin2 (βarr2) mount a reduced hyperlocomotor response to either morphine or amphetamine. However, mice deficient in GSK3β in D2R-expressing neurons show a significantly reduced locomotor response to only amphetamine but not morphine. Interestingly, all mice tested show a normal CPP response to either morphine or amphetamine. β-arrestin-mediated DA receptor signalling has an important role in the locomotor response, but not CPP, to drugs such as morphine and amphetamine, demonstrating a functional selectivity of DA-dependent behaviours in mice. It is likely that G-protein-dependent signalling through DA receptors mediates the CPP response.

SUBMITTER: Urs NM

PROVIDER: S-EPMC4850582 | biostudies-other | 2014 Jul

REPOSITORIES: biostudies-other

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Project description:Functional selectivity (or biased agonism) is a property exhibited by some G protein-coupled receptor (GPCR) ligands, which results in the modulation of a subset of a receptor's signaling capabilities and more precise control over complex biological processes. The dopamine D2 receptor (D2R) exhibits pleiotropic responses to the biogenic amine dopamine (DA) to mediate complex central nervous system functions through activation of G proteins and β-arrestins. D2R is a prominent therapeutic target for psychological and neurological disorders in which DA biology is dysregulated and targeting D2R with functionally selective drugs could provide a means by which pharmacotherapies could be developed. However, factors that determine GPCR functional selectivity in vivo may be multiple with receptors, ligands and transducers contributing to the process. We have recently described a mutagenesis approach to engineer biased D2R mutants in which G protein-dependent ([Gprot]D2R) and β-arrestin-dependent signaling ([βarr]D2R) were successfully separated (Peterson, et al. PNAS, 2015). Here, permutations of these mutants were used to identify critical determinants of the D2R signaling complex that impart signaling bias in response to the natural or synthetic ligands. Critical residues identified in generating [Gprot]D2R and [βarr]D2R conferred control of partial agonism at G protein and/or β-arrestin activity. Another set of mutations that result in G protein bias was identified that demonstrated that full agonists can impart unique activation patterns, and provided further credence to the concept of ligand texture. Finally, the contributions and interplay between different transducers indicated that G proteins are not aberrantly activated, and that receptor kinase and β-arrestin activities are inextricably linked. These data provide a thorough elucidation of the feasibility and malleability of D2R functional selectivity and point to means by which novel in vivo therapies could be modeled.

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The physiological relevance of functional selectivity in dopamine signalling.

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